For those of you that remember my thread about nasty sound from my PC usb port to the 990's usb port, here is an update I'd like to share with you all.
I bought this little M-Audio transit audio upgrade unit:
http://www.jr.com/JRProductPage.process?Product=3719104

What an overall difference it has made! The sound is much smoother and because I have it hooked via optical, the ground loop humm is gone.

It does bring up a question that I hope someone can answer.
There are 4 settings on the card but the 2 that apply are:
1. 0 in 2 out 88,2200Hz - 96,000Hz (in this mode I get only PCM 96/24, Upsample and Bypass.

Why can't I get 5/7ch Stereo?

2. 2 in 2 out 8000hz- 48,000hz, I can get all the modes.
What's the difference in these two settings?

I'm not sure about exactly what the descriptions are referring to, but it sounds like option 1 is outputting 96kHz rather than the standard 44.1kHz to 48kHz. Processing audio at that rate (which is the same as normal inputs with upsample applied in the 990) takes a big bite out of the 990's processing power, and I suspect that's why it doesn't give you access to 5/7 Stereo or matrix processing modes like Pro Logic IIx or NEO:6. The second option is the normal CD quality sound, which the 990 can do whatever you want to with. At least that's my best guess...

Gonk, thanks. Any thoughts on why this little unit improved the sound quality so much?

I am just curious. I was under the impression that the 990 acted as one large sound card when connected from usb to usb but not sure why this card produced better results.

Hmmm... I don't know much about how the USB audio input is actually implemented on the 990 - it may be a driver issue between your PC and the 990, or an issue with the USB ports on your PC, or something else entirely - so it's hard for me to say just what originally led to your USB input's poor audio performance. Clearly it was somewhere in the USB chain (PC's USB controller, USB drivers of some sort, or the 990's USB input)...

My guess on the better sound quality has to do with the drivers and hardware associated with the m-audio device. I use a few usb based "professional" audio devices and each one sounds different, and reacts different to different software. I find m-audio to be better than most. The standard windows drivers for audio on usb are terrible.
The difference between mode 1 and 2 from the m-audio perspective has to do with usb bandwidth and control. USB just can't handle 24/96 at 2 channels in and out. So you get just out.
As for the 990, I'm not sure but I suspect a similar reason to what gonk has said, essential bandwidth and processing power.
BTW the reason for the quotes on professional above is that some devices can't even get the drivers correct after 2 years. Not very professional at all.

This is slightly off topic, but Maudio also makes a pcmcia audio card for laptops and its also great.