All of the features of my new Sonar X3 DAW seem to be fully functional, except that I'm experiencing severe and frequent dropout problems. I've optimized my system for recording by setting my computer's power for high performance and setting both my minimum and maximum 'plugged in' processor states to 100% (to avoid CPU throttling issues), disabled my system sounds, and set my processor scheduling to "background services".
 
I'm using a Toshiba Satellite S855 with an Intel core i7-3630QM @ 2.40GHz. 7.89 GB usable RAM. 64-bit Windows 8 with x64 based processor, a Focusrite 18i20, and the 64 bit version of Sonar X3. I've got my ASIO panel (MixControl) set to the maximum buffer of 20ms, and recording and playback both set to 256ms in Sonar. The Dropoutmsec variable in Sonar is currently set at the standard 250.
 
I've used the program LatencyMon to collect data while I record and experience dropouts. The data pointed me towards the Kernel Driver in my computer, which led me to suspect conflict between my Focusrite 18i20 (which I record with via USB), and my Allen & Heath Zed 18 mixing board (which I always kept connected to my computer via USB). As a result, I disconnected the Allen & Heath before attempting to record again, however the dropout problem persisted. I ran yet another LatencyMon test with the Allen & Heath disconnected, in which I recorded drums through the 18i20 until a dropout occurred, the results of which I've included below.
 
I had been connecting the Focusrite 18i20 through a USB 3.0 port, so I just ran another test (in which I recorded drums until a dropout occurred) with the 18i20 connected through a 2.0 port. The results are below as well.
 
Any further advice would be fantastic!

After disconnecting the mixer:
 
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CONCLUSION
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Your system appears to be having trouble handling real-time audio and other tasks. You are likely to experience buffer underruns appearing as drop outs, clicks or pops. One or more ISR routines that belong to a driver running in your system appear to be executing for too long. One problem may be related to power management, disable CPU throttling settings in Control Panel and BIOS setup. Check for BIOS updates.
LatencyMon has been analyzing your system for 0:01:42 (h:mm:ss) on all processors.

_________________________________________________________________________________________________________
SYSTEM INFORMATION
_________________________________________________________________________________________________________
Computer name: RICKYSLAPTOP
OS version: Windows 8 , 6.2, build: 9200 (x64)
Hardware: Satellite S855, TOSHIBA, Portable PC
CPU: GenuineIntel Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
Logical processors: 8
Processor groups: 1
RAM: 8076 MB total

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CPU SPEED
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Reported CPU speed: 2395.0 MHz
Measured CPU speed: 2026.0 MHz (approx.)
Note: reported execution times may be calculated based on a fixed reported CPU speed. Disable variable speed settings like Intel Speed Step and AMD Cool N Quiet in the BIOS setup for more accurate results.

_________________________________________________________________________________________________________
MEASURED INTERRUPT TO USER PROCESS LATENCIES
_________________________________________________________________________________________________________
The interrupt to process latency reflects the measured interval that a usermode process needed to respond to a hardware request from the moment the interrupt service routine started execution. This includes the scheduling and execution of a DPC routine, the signaling of an event and the waking up of a usermode thread from an idle wait state in response to that event.
Highest measured interrupt to process latency (µs): 303.620309
Average measured interrupt to process latency (µs): 5.150816
Highest measured interrupt to DPC latency (µs): 280.100426
Average measured interrupt to DPC latency (µs): 1.251752

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REPORTED ISRs
_________________________________________________________________________________________________________
Interrupt service routines are routines installed by the OS and device drivers that execute in response to a hardware interrupt signal.
Highest ISR routine execution time (µs): 562468.767850
Driver with highest ISR routine execution time: i8042prt.sys - i8042 Port Driver, Microsoft Corporation
Highest reported total ISR routine time (%): 0.167453
Driver with highest ISR total time: Wdf01000.sys - Kernel Mode Driver Framework Runtime, Microsoft Corporation
Total time spent in ISRs (%) 0.127490
ISR count (execution time <250 µs): 579501
ISR count (execution time 250-500 µs): 0
ISR count (execution time 500-999 µs): 0
ISR count (execution time 1000-1999 µs): 0
ISR count (execution time 2000-3999 µs): 0
ISR count (execution time >=4000 µs): 0

_________________________________________________________________________________________________________
REPORTED DPCs
_________________________________________________________________________________________________________
DPC routines are part of the interrupt servicing dispatch mechanism and disable the possibility for a process to utilize the CPU while it is interrupted until the DPC has finished execution.
Highest DPC routine execution time (µs): 362.288935
Driver with highest DPC routine execution time: Wdf01000.sys - Kernel Mode Driver Framework Runtime, Microsoft Corporation
Highest reported total DPC routine time (%): 0.186164
Driver with highest DPC total execution time: Wdf01000.sys - Kernel Mode Driver Framework Runtime, Microsoft Corporation
Total time spent in DPCs (%) 0.225216
DPC count (execution time <250 µs): 756767
DPC count (execution time 250-500 µs): 0
DPC count (execution time 500-999 µs): 1611
DPC count (execution time 1000-1999 µs): 0
DPC count (execution time 2000-3999 µs): 0
DPC count (execution time >=4000 µs): 0

_________________________________________________________________________________________________________
REPORTED HARD PAGEFAULTS
_________________________________________________________________________________________________________
Hard pagefaults are events that get triggered by making use of virtual memory that is not resident in RAM but backed by a memory mapped file on disk. The process of resolving the hard pagefault requires reading in the memory from disk while the process is interrupted and blocked from execution.
NOTE: some processes were hit by hard pagefaults. If these were programs producing audio, they are likely to interrupt the audio stream resulting in dropouts, clicks and pops. Check the Processes tab to see which programs were hit.
Process with highest pagefault count: chrome.exe
Total number of hard pagefaults 83
Hard pagefault count of hardest hit process: 75
Highest hard pagefault resolution time (µs): 1192702.685595
Total time spent in hard pagefaults (%): 0.199579
Number of processes hit: 3

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PER CPU DATA
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CPU 0 Interrupt cycle time (s): 7.754258
CPU 0 ISR highest execution time (µs): 562468.767850
CPU 0 ISR total execution time (s): 1.040316
CPU 0 ISR count: 579502
CPU 0 DPC highest execution time (µs): 362.288935
CPU 0 DPC total execution time (s): 1.805143
CPU 0 DPC count: 754556
_________________________________________________________________________________________________________
CPU 1 Interrupt cycle time (s): 3.571119
CPU 1 ISR highest execution time (µs): 0.0
CPU 1 ISR total execution time (s): 0.0
CPU 1 ISR count: 0
CPU 1 DPC highest execution time (µs): 22.560752
CPU 1 DPC total execution time (s): 0.000115
CPU 1 DPC count: 40
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CPU 2 Interrupt cycle time (s): 1.483513
CPU 2 ISR highest execution time (µs): 0.0
CPU 2 ISR total execution time (s): 0.0
CPU 2 ISR count: 0
CPU 2 DPC highest execution time (µs): 151.631733
CPU 2 DPC total execution time (s): 0.012879
CPU 2 DPC count: 1324
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CPU 3 Interrupt cycle time (s): 2.906584
CPU 3 ISR highest execution time (µs): 0.0
CPU 3 ISR total execution time (s): 0.0
CPU 3 ISR count: 0
CPU 3 DPC highest execution time (µs): 25.059708
CPU 3 DPC total execution time (s): 0.000290
CPU 3 DPC count: 80
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CPU 4 Interrupt cycle time (s): 1.689829
CPU 4 ISR highest execution time (µs): 0.0
CPU 4 ISR total execution time (s): 0.0
CPU 4 ISR count: 0
CPU 4 DPC highest execution time (µs): 154.588309
CPU 4 DPC total execution time (s): 0.010349
CPU 4 DPC count: 1172
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CPU 5 Interrupt cycle time (s): 3.022037
CPU 5 ISR highest execution time (µs): 0.0
CPU 5 ISR total execution time (s): 0.0
CPU 5 ISR count: 0
CPU 5 DPC highest execution time (µs): 28.325678
CPU 5 DPC total execution time (s): 0.000620
CPU 5 DPC count: 150
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CPU 6 Interrupt cycle time (s): 1.590594
CPU 6 ISR highest execution time (µs): 0.0
CPU 6 ISR total execution time (s): 0.0
CPU 6 ISR count: 0
CPU 6 DPC highest execution time (µs): 149.844676
CPU 6 DPC total execution time (s): 0.008177
CPU 6 DPC count: 996
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CPU 7 Interrupt cycle time (s): 2.968890
CPU 7 ISR highest execution time (µs): 0.0
CPU 7 ISR total execution time (s): 0.0
CPU 7 ISR count: 0
CPU 7 DPC highest execution time (µs): 19.546973
CPU 7 DPC total execution time (s): 0.000194
CPU 7 DPC count: 60
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Attempted with a USB 2.0 port rather than 3.0
 
_________________________________________________________________________________________________________
CONCLUSION
_________________________________________________________________________________________________________
Your system appears to be suitable for handling real-time audio and other tasks without dropouts.
LatencyMon has been analyzing your system for 0:02:42 (h:mm:ss) on all processors.

_________________________________________________________________________________________________________
SYSTEM INFORMATION
_________________________________________________________________________________________________________
Computer name: RICKYSLAPTOP
OS version: Windows 8 , 6.2, build: 9200 (x64)
Hardware: Satellite S855, TOSHIBA, Portable PC
CPU: GenuineIntel Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
Logical processors: 8
Processor groups: 1
RAM: 8076 MB total

_________________________________________________________________________________________________________
CPU SPEED
_________________________________________________________________________________________________________
Reported CPU speed: 2395.0 MHz
Measured CPU speed: 2024.0 MHz (approx.)
Note: reported execution times may be calculated based on a fixed reported CPU speed. Disable variable speed settings like Intel Speed Step and AMD Cool N Quiet in the BIOS setup for more accurate results.

_________________________________________________________________________________________________________
MEASURED INTERRUPT TO USER PROCESS LATENCIES
_________________________________________________________________________________________________________
The interrupt to process latency reflects the measured interval that a usermode process needed to respond to a hardware request from the moment the interrupt service routine started execution. This includes the scheduling and execution of a DPC routine, the signaling of an event and the waking up of a usermode thread from an idle wait state in response to that event.
Highest measured interrupt to process latency (µs): 246.317321
Average measured interrupt to process latency (µs): 5.014379
Highest measured interrupt to DPC latency (µs): 180.461648
Average measured interrupt to DPC latency (µs): 1.271723

_________________________________________________________________________________________________________
REPORTED ISRs
_________________________________________________________________________________________________________
Interrupt service routines are routines installed by the OS and device drivers that execute in response to a hardware interrupt signal.
Highest ISR routine execution time (µs): 130.096033
Driver with highest ISR routine execution time: i8042prt.sys - i8042 Port Driver, Microsoft Corporation
Highest reported total ISR routine time (%): 0.013587
Driver with highest ISR total time: USBPORT.SYS - USB 1.1 & 2.0 Port Driver, Microsoft Corporation
Total time spent in ISRs (%) 0.013734
ISR count (execution time <250 µs): 25216
ISR count (execution time 250-500 µs): 0
ISR count (execution time 500-999 µs): 0
ISR count (execution time 1000-1999 µs): 0
ISR count (execution time 2000-3999 µs): 0
ISR count (execution time >=4000 µs): 0

_________________________________________________________________________________________________________
REPORTED DPCs
_________________________________________________________________________________________________________
DPC routines are part of the interrupt servicing dispatch mechanism and disable the possibility for a process to utilize the CPU while it is interrupted until the DPC has finished execution.
Highest DPC routine execution time (µs): 879.666806
Driver with highest DPC routine execution time: storport.sys - Microsoft Storage Port Driver, Microsoft Corporation
Highest reported total DPC routine time (%): 0.045066
Driver with highest DPC total execution time: USBPORT.SYS - USB 1.1 & 2.0 Port Driver, Microsoft Corporation
Total time spent in DPCs (%) 0.159669
DPC count (execution time <250 µs): 220585
DPC count (execution time 250-500 µs): 0
DPC count (execution time 500-999 µs): 3
DPC count (execution time 1000-1999 µs): 0
DPC count (execution time 2000-3999 µs): 0
DPC count (execution time >=4000 µs): 0

_________________________________________________________________________________________________________
REPORTED HARD PAGEFAULTS
_________________________________________________________________________________________________________
Hard pagefaults are events that get triggered by making use of virtual memory that is not resident in RAM but backed by a memory mapped file on disk. The process of resolving the hard pagefault requires reading in the memory from disk while the process is interrupted and blocked from execution.
NOTE: some processes were hit by hard pagefaults. If these were programs producing audio, they are likely to interrupt the audio stream resulting in dropouts, clicks and pops. Check the Processes tab to see which programs were hit.
Process with highest pagefault count: sonarx3.exe
Total number of hard pagefaults 80
Hard pagefault count of hardest hit process: 74
Highest hard pagefault resolution time (µs): 395066.676827
Total time spent in hard pagefaults (%): 0.186917
Number of processes hit: 3

_________________________________________________________________________________________________________
PER CPU DATA
_________________________________________________________________________________________________________
CPU 0 Interrupt cycle time (s): 8.963876
CPU 0 ISR highest execution time (µs): 130.096033
CPU 0 ISR total execution time (s): 0.178007
CPU 0 ISR count: 25216
CPU 0 DPC highest execution time (µs): 298.505637
CPU 0 DPC total execution time (s): 1.899299
CPU 0 DPC count: 201209
_________________________________________________________________________________________________________
CPU 1 Interrupt cycle time (s): 1.754151
CPU 1 ISR highest execution time (µs): 0.0
CPU 1 ISR total execution time (s): 0.0
CPU 1 ISR count: 0
CPU 1 DPC highest execution time (µs): 33.264301
CPU 1 DPC total execution time (s): 0.001731
CPU 1 DPC count: 214
_________________________________________________________________________________________________________
CPU 2 Interrupt cycle time (s): 1.487311
CPU 2 ISR highest execution time (µs): 0.0
CPU 2 ISR total execution time (s): 0.0
CPU 2 ISR count: 0
CPU 2 DPC highest execution time (µs): 879.666806
CPU 2 DPC total execution time (s): 0.037981
CPU 2 DPC count: 4364
_________________________________________________________________________________________________________
CPU 3 Interrupt cycle time (s): 2.229057
CPU 3 ISR highest execution time (µs): 0.0
CPU 3 ISR total execution time (s): 0.0
CPU 3 ISR count: 0
CPU 3 DPC highest execution time (µs): 58.243424
CPU 3 DPC total execution time (s): 0.002533
CPU 3 DPC count: 343
_________________________________________________________________________________________________________
CPU 4 Interrupt cycle time (s): 1.495404
CPU 4 ISR highest execution time (µs): 0.0
CPU 4 ISR total execution time (s): 0.0
CPU 4 ISR count: 0
CPU 4 DPC highest execution time (µs): 138.677244
CPU 4 DPC total execution time (s): 0.027181
CPU 4 DPC count: 3363
_________________________________________________________________________________________________________
CPU 5 Interrupt cycle time (s): 2.355847
CPU 5 ISR highest execution time (µs): 0.0
CPU 5 ISR total execution time (s): 0.0
CPU 5 ISR count: 0
CPU 5 DPC highest execution time (µs): 78.554906
CPU 5 DPC total execution time (s): 0.003786
CPU 5 DPC count: 475
_________________________________________________________________________________________________________
CPU 6 Interrupt cycle time (s): 1.605092
CPU 6 ISR highest execution time (µs): 0.0
CPU 6 ISR total execution time (s): 0.0
CPU 6 ISR count: 0
CPU 6 DPC highest execution time (µs): 82.406681
CPU 6 DPC total execution time (s): 0.090242
CPU 6 DPC count: 9784
_________________________________________________________________________________________________________
CPU 7 Interrupt cycle time (s): 2.489387
CPU 7 ISR highest execution time (µs): 0.0
CPU 7 ISR total execution time (s): 0.0
CPU 7 ISR count: 0
CPU 7 DPC highest execution time (µs): 47.356159
CPU 7 DPC total execution time (s): 0.006751
CPU 7 DPC count: 836
_________________________________________________________________________________________________________
 

Hardware is my weakest area but while waiting on the experts....
 
It is unclear if this is an audio dropout or MIDI missing notes issue. If this is audio, how many tracks are being recorded. The sample rate might also be useful.
 
But while awaiting clarification, just a few notes.
 
Setting the processor scheduling to "background services" is usually not recommended for SONAR although it has been claimed to be a benefit by some. If there was more optimization done than was indicated above, it may be a good idea to undo it. A lot of optimization is not needed from Win7 on and some can make performance worse.
 
There is no harm in doubling or tripling the Dropoutmsec variable.
 
Neither device is USB3, usually it is not recommended to use USB3 ports for USB2 audio interfaces. IIRC the Allen & Heath Zed 18 is a USB1 device.

Audio dropout, no midi involved here. Currently I've been attempting to record just 3 channels simultaneously, with no effects applied. 44.1kHz sample rate.

Are you trying to do everything on the 5400RPM system drive?

Currently, yes.

I do have access to an unused 7200RPM, 320GB, USB 2.0 external drive. Would that take the load off my system drive?

Not crazy about using USB2 drives for project data but it may be better than the current setup. You could also try tweaking  the playback and record buffers in Preferences > Audio > Sync and Caching. Adjust the values up in 128MB increments.

I'll play around with the buffers and then give the external drive a shot if the problem persists. If I were to connect the external drive, which components should I move over to it?