Just a status update on this issue re: Omnimic. The "fix" above worked wonderfully when I first applied it. However, opened up Omnimic yesterday, plugged the mic in, and it was 20 dB TOO HIGH.
I went in and unapplied the fix, tested and was again 20 dB too low. Went back to the executable, reapplied the win XP compatibility mode and everything was spot on again.
I have no idea what's going on, but it's screwy.
Also, I have the UMIK-1 USB mic setup with REW on same laptop and no issues with SPL.
Just an FYI