I have my Mac Mini (Core Duo 1.8) connected to one of the DVI inputs of the 990, and it passes the signal to my HD LCD display just fine. If you can use one of the DVI inputs or connect it directly to an input on your display, you'll obviously get a better picture.
FYI - the 990 will not lock onto the Mac's digital audio signal when the Mac is outputting DTS. Hopefully this incompatibility will be considered during the development of the next gen processor... hopefully...
- Jason