Ian,

I have the M-Audio Revolution 7.1 Sound card connected via a 35ft Accell Cables Digital Coax. I am using my Old DAC from 1992. which has an advance clock from those early days.

I took the cable off of the 1070 so I can use my tube Preamp. I have done research about SPDIF vs. USB and for my situation, I must use SPDIF. I did visit somone who what hook up his Mac laptop via USB to the new Bel Canto 3 DAC/Pre ($2500)and the sound was great.

Is theory, the USB was designed for data while the SPDIF was for Audio. USB over a short run going into a DAC that has a lot of attention to re-clock the signal (Bel Canto, Benchmark Dac1) has one thing over SPDIF. The USB is native to the OS while the sound card using drivers. The drivers add one more layer.

All things being equal, I am told be an enginner that they both will work equal.

IMHO, should you use an external DAC that is high end in it's design (see above) you will get better SQ that the 990. I may trade in my old DAC for a more current unit that has 24bit Dacs. I will use any DAC only for my PC sound. I like what I read about the Benchmark and is it made by a company that does Pro Audio.

Keep in touch and let me know what you do.

Liz