Just replaced my Cakewalk US-25EX with this new unit.. installed most up to date driver and firmware. Getting crackling noise when I am trying to record an instrument. 
I must be missing something in the settings. ASIO is set to lowest, if I change it to 256 sampling rate, then no noise, but latency is there. Any help would be greatly appreciated. On a deadline :-)

The crackling is from too low a latency - it is drawing too much on the CPU.  Which is silly, considering your computer.  You should be able to get much lower latency.   Try disabling the wireless and start working your way through optimizing your computer.
 
@

OK - what are the Sonar-reported latency values from Edit>Preferences>Audio>Driver Settings?
 
Also, in this particular project, do you have any effects loaded?  If so, hit 'E' on your computer keyboard to toggle off/on the bypass all effects, and then see if the crackles go away with your ASIO Buffer Size back down at 128.
 
IF the crackles go away with your effects bypassed, then you have one or more effects that are messing things up - and likely are meant for use in mixing rather than for recording.
 
Bob Bone
 

Go to the Windows control panel and open the UX-2x2 settings; the ASIO control panel will show the firmware and driver. Make absolutely sure it shows driver 1.01 and firmware 1.01; if not, got to the US-2x2 downloads page. Crackling was a known issue with 1.00 drivers and firmware if there was heavy plug-in loading. 
 
Also check the release notes. You have to install the driver first as that's what shuttles the firmware into the unit. If you do it the other way around, the firmware may appear to have been loaded but the only way to know for sure is to check the control panel.
 
I don't know how complex your project is, which of course will make a difference with how much latency the system will attain, but I've been running at 128 samples on a fairly complex project for the past several days with some CPU-hungry instruments and FX chains...no issues. However, 64 samples wasn't doable.
 
Also check out this tip from the Tip of the Week thread. For some systems it makes a major improvement, others not so much but there's no downside to trying it.