Tripecac
I just tried Sonar, and after about 10 minutes the problem happened again.  I restarted Sonar, and again it happened after a few minutes.
 
To clarify, when I say "dropout" in this topic I mean the sound completely stops, and doesn't come back until I restart Sonar.  It's not like a momentary dropout, a short interruption in the sound (usually resulting in a pop or click).  This is a complete cessation of audio, probably from either the Sonar audio engine or the ASIO driver.
 
My sample rate in Sonar is 44 kHz.  The Audio Driver Bit Depth is greyed out, but says "24".  I cannot change that value.  Samples are 256, with an effective latency of 5.8 ms.
 
I forgot about the M-Audio and Xonar cards.  I have now disabled them using the Device Manager.  However, within about 2 minutes, the problem came again.
 
I notice that the CPU activity is high.
 
Also, changing the ASIO from 256 to 128 samples (and back) does not fix the problem.  But maybe that doesn't really reset the ASIO driver.
 
I'll give the beta drivers a shot.

As well as disabling the M-Audio and Xonar cards, you should remove all trace of their drivers, both at program level and also in the Registry

Tripecac
 
My sample rate in Sonar is 44 kHz.  The Audio Driver Bit Depth is greyed out, but says "24".  I cannot change that value.  Samples are 256, with an effective latency of 5.8 ms.
 
I forgot about the M-Audio and Xonar cards.  I have now disabled them using the Device Manager.  However, within about 2 minutes, the problem came again.
 
I notice that the CPU activity is high.
 
Also, changing the ASIO from 256 to 128 samples (and back) does not fix the problem.  But maybe that doesn't really reset the ASIO driver.
 
I'll give the beta drivers a shot.

Hi. Are you tracking, or mixing?
If you are mixing, try doubling latency from 256, to 512 (or 1024) and see if it helps. 
If you are tracking, use low latency, and / or press "E", to bypass all fx, if problems with engine stopping. 
Switch back and forth when tracking / mixing.
All the best.

I am having the same issue for some weeks now. I disabled "suspend audio engine when sonar is not in focus", it seems to help a little bit. 
I hope it helps. 

Tripecac
I've been using Drumlab for the first time (since it was in Komplete 11, which I got recently).  It sounds great, but I notice it uses about 30-35 voices, which seems a bit high for a Komplete Instrument.
 
If I increase the ASIO buffer from 256 to 2048 the latency would go from 5.8ms to 46.4ms, which is pretty horrible for tracking (but okay for mixing).  Are you suggesting doing it as a test only, not a permanent change?

Yes for testing only. It will either confirm or rule out it being caused by a plugin or process hogging resources.
 
I did once have a very similar issue which I am pretty certain involved Drumlab and or an effect plugin I had on a bus that drumlab was going through. This could be related. So here's what I did. I firstly did a save as... and on that copy I went through removing plugins (instruments and effects) one by one until I found the culprit, which I am pretty sure was drumlab or the effect. So I kept the midi that was playing drumlab, removed drumlab completely from the project, then inserted a fresh instance of drumlab. THat fixed it for me.

Tripecac, I have a problem with my 2i2 and just got Sonar professional. Finally Focusrite got back to me and asked me to try a different DAW. I installed the demos of FL Studio and Reaper and the Focusrite worked flawlessly. I started up Sonar again and no go. It just clicks and pops. So apparently there is a problem between focusrite drivers and Sonar. Not sure what to do now because Ive used Sonar for so many years and don't want to get rid of it but I'm not going to keep buying usb audio devices to find they don't work with sonar. I would say try downloading a demo of another DAW and see if it still does it or not.

Jengelh71
Tripecac, I have a problem with my 2i2 and just got Sonar professional. Finally Focusrite got back to me and asked me to try a different DAW. I installed the demos of FL Studio and Reaper and the Focusrite worked flawlessly. I started up Sonar again and no go. It just clicks and pops. So apparently there is a problem between focusrite drivers and Sonar. Not sure what to do now because Ive used Sonar for so many years and don't want to get rid of it but I'm not going to keep buying usb audio devices to find they don't work with sonar. I would say try downloading a demo of another DAW and see if it still does it or not.

That doesn't really prove anything as there are lots of people using Focusrite AIs with Sonar without issues and people using Focusrite AIs with other DAWs and having problems. So on your system/Sonar configuration, there's a problem.

Never said it proves anything. But instead of being in that "sonar is the best, it cant be sonar" state of mind, process of elimination usually works. Just saying he should try another daw and if it does the same, maybe his usb audio is no good. In my case there is a sonar problem, because it works fine on sonar 8.5. Just not professional. So Tripecac disregard what i said and keep chasing your tail because obviously I'm not allowed to try and help with suggestions.

I was having some drop out issues with my Focusrite 2i4 for a while there. It happens now and again...sometimes projects corrupt because of it. Anyway so far so good with the newer driver.
 

The audio just crashed again, forcing me to restart SONAR.  And then it happened again.
 
Changing the ASIO buffers from 256 to 512 did not help.
Disabling "Suspend Audio Engine when SONAR is not in focus" did not help either.
 
I then enabled Plug-In Load Balancing.  And in a few minutes it crashed again.
 
I then switch the driver mode from ASIO to WDM, and got a blue screen of death!  In other words, Windows 7 COMPLETELY crashed, so I had to reboot the computer!  The error code was: DRIVER_IRQL_NOT_LESS_OR_EQUAL.  Wow!  I haven't seen a BSOD in years!
 
Fortunately, the computer crashed before SONAR could save the change from ASIO to WDM.
 
 
 

I just noticed something very strange, and it could just be a coincidence.
 
After I stopped working on my project, I ran my usual backup script, which uses rysync to backup my project files locally and remotely.  I've been using the same script for more than 10 years, but for some reason, for the first time ever, rsync failed, giving me a STATUS_ACCESS_VIOLATION error.  I tried again, as administrator, and got the same error.  It didn't matter if I was rsyncing locally or remotely.
 
I then restarted windows, and tried again.  This time it worked.
 
Could the rsync issue possibly be related to the Sonar/Focusrite issue???  Again, this is the first time I've ever seen rsync fail like that, and the only thing I've done since rebooting earlier (after the BSOD) was use Sonar.