I've just recently purchased the same Pioneer unit and have been playing with it for a few hours now. My impression of the difference between the DAC in the Pioneer vs the DAC in my Yamaha rxv450 is as follows; the coax sounds like a great home theater, the 5.1 sounds like a movie theater. Can't quite put my finger on why, but there seems to be a lot more depth, clarity, precision etc. Much more dynamic. This despite the lack of output level control for the separate channels.

Even more stunning is the difference between the DAC in the Pioneer vs the one in my crap KLH $50 5-disc cd player which it replaces. Pretty amazing how much info was lost using the KLH. I swear it didn't even have even frequency response.