If you have a dock that offers a digital output, I'd suggest starting out by just going directly to the 990 with a digital cable - the 990 has a pretty respectable DAC already, and I've used it for CD's with very pleasant results. If you are using any sort of lossy compression (no matter how good) or if you ever use any surround processing with music (PLIIx, NEO:6, or 5/7 Stereo), I'd definitely hold off on investing additional money in an outboard DAC. I think the idea of a dock with digital out and a DAC is most often used for two-channel systems, as good two-channel setups are often based around analog receivers or pre-amps.