Before anyone suggests it, I cannot update Sonar because I'm blind and the later versions of Sonar will not work with the JAWS screenreader.
 
I just had to update my hardware, so am setting up this particular machine. Am running Win 7 Home Premium, 64 bit. Sonar 8.5.3. Sample setting 44100/16 bit, so nothing esoteric here!
 
Hardware manager sees the mixer as "USB Codec", so Windows knows the thing exists.
 
Recording ANYTHING gives me very glitchy audio - have experimented with different buffer sizes to no effect. Have tried all the driver options, but only WDM sees the mixer. ASIO4all only sees the Realtek audio inputs on the motherboard - they are not high enough quality for what I do.
 
The odd thing is that iTunes will play back audio just fine - so the system seems to be happy with the mixer, but Sonar isn't. Sound Forge has the same problem.
 
Any suggestions for settings or other things to look at?
 

First  are using the USB 2 version? If so then you need specific drivers (not class compliant). USB Codec is a strange name for an interface driver. Check properties for what you think is the driver in device manager. If it says it is working properly, that is reassuring. If it says drivers have not been installed, then you need to install them.
The first suggestion is to check for the latest driver for your interface. Apparently it shipped with XP and Vista drivers but there is a driver available for Win XP through Win 10 that may have better support for newer computers. There is also a firmware update on their site that might be worth trying. USB Codec is a strange name for an interface driver. Another thing to check is whether you are trying to use it in a USB 3 socket. Try plugging it into different sockets. Sometimes equipment designed for USB 2 does not play well with USB 3 controllers.
 
http://www.alesis.com/products/view/multimix-8-usb-2.0
 
 
 

My Behringer  USC 200 interface I use for live playback uses the USB audio codex driver. Sonar sees it as a WDM/KS driver which is at least better than MME mode. The USB codex is obviously a native windows WDM driver. The device is instantly recognised by any computer. I have never had to change the audio setting when I hook it up. It just always works without fuss..
 
But that's playback.  
It will also work just fine for a stereo board mix recording, even into Sonar.  
But multi track overdub recording will result in unstable offset timing. Your tracks will not sync with each other. 
An forget asio4all that doesn't work either as it's still WDM mode even though they call it asio.  
 
The USB offerings of most mixing boards are just fine for music playback and recording a stereo mix of your gigs. But they fall short for multi track recording because of the timing issue. Yamaha mixers use Steinberg ASIO drivers and I'm sure a few other brands are now offering proper ASIO drivers too. 
 
Sonar is only happy when you use good ASIO drivers. All other drivers will cause issues like you are experiencing. 
 
Make sure you run the Wave Profiler.