Sonarworks Reference Measure for Windows uses Direct Sound drivers. Most sound cards support Direct Sound.
Make sure you have set your hardware to 44.1 kHz sample rate. Otherwise the software will not work.
Yes we support AVID Omni and other AVID sound cards! They work, you only need to change the sample rate to 44.1 kHz. You also need to make sure the AVID sound card is available outside Pro Tools!
Also, we've encountered some situations where the buffer size needs to be set to lower values (some MOTU devices have issues with 1024, setting it to anything lower works fine).
It's worth checking that you don't have any input channel panning happening if you use device with multiple input channels.
If you still encounter problems please submit a request here.