Five0SixBand
Prob a long shot but does anyone here use this combination?
I use it - and it works fine. I just check the MOTU site every once in a while for the latest drivers (I don't even remember if they're technically for Win 8 or not) - but it works fine.
PS - Win 8.1 pro 64 bit, and SONAR X3b (soon to be X3c) 64 bit - is my setup.