I'm wondering the same thing. I have an Adcom GDA 600 (DAC) that uses a Burr-Brown. Since I'm still running only Dolby ProLogic gear (unitl I get my 990!) I have been, for years, using the GDA 600 as the DAC for my CD player and DVD player (until I moved my combo Tivo/DVD player to my regular TV since getting my HD RPTV that is). I would run the toslink from the DVD player into my DAC, as well as the S/PDIF coax from my CD player. But now, when I get the 990, I'll obviously use that to decode DVD audio (I'm getting the Oppo DVD player). But, if I don't like the way the 990 decodes the CD stream, I'll just continue to use my seperate DAC unit to do that. You should still be able to get some quasi surround modes out of the 990 even with just stereo analogue input from the seperate DAC...right? I can at least with my current Adcom preamp, a 10 yr old GTP-600. Besides, I enjoy listening to CD's in 2 channel stereo anyway.

But, I am currious as to which is the better DAC.
According to my GDA 600 manual, the specs are:

Input decoding...........Crystal CS 8412 receiver
Digital filter............Burr-Brown Linear Phase
Resampling rate.....8x(352.8khz for 44.1khz input)
DAC type..........selected R-2R Burr-Brown PCM-63
resolution................................20 bits

I guess no one can know until they release the specs. I ain't too smart, so maybe someone could enlighten me on whether my GDA-600 has been overtaken in the last 10 years since I bought it by better designs that are cheap and common (and thus, most likely included within the 990).

All I know is that CD's sound great with my current setup, and when I would switch the audio input on my preamp between the analogue output of the DVD player and the analogue output of the GDA 600, I could tell a distinct difference...I could do this as the movie was playing by just changing the source of the audio input...the GDA-600 gave crisper, cleaner highs (of course, I'm sure the audio DAC in my Hitachi Tivo/DVD combo unit is not the greatest).