im having the exact same problem, did you just get yours? My came in the mail on Wednesday, maybe we got a bad batch. I do all the right things but no sound. I'll unplug the 990, and plug in my sm58 and it works fine. I noticed my mic doesn't have the little cartoid symbol on it, dunno. I may send it back if I can't figure it out soon - seems to just not work.
Make/Model: MAC PPC G4 Dual 867mhz
Operating System: OSX 10.4.11
M-Audio Devices & Driver Versions:
Fast Track Pro
Axiom Pro 49