Lot's of good info there. A few followup questions/comments:

1) "Again, we can only get the most from the weakest link along the chain, not just the DAC, nor just the 990, but cable and wires."

Seems like another argument for using digital (no need to invest in expensive interconnects). My $4 optical cable, courtesy ebay, is working just fine. As somebody pointed out, if the bits get there, they get there.

2) "...I listen to it (upsampling) using analog inputs. and it sounds really good."

I too have listened to the 990 in upsample mode, with analog inputs. It does work, and sounds good... but I'm not sure exactly what it is that I'm listening too. Are we doing a A->D conversion, and then "upsampling" that before converting back to analog? Maybe one of the outlaw guys can clue us in a bit more on how this works.

3) "...format in question only allows analog output (which would be the case for SACD and DVD-Audio)."

Is the 5.1 "DVD audio" encoding fundamentally different than that used for 5.1 DVD movies? I get 5.1 sound just fine for movies using the optical cable. And I have a couple dual-disc CD/DVD's that seem to give me 5.1 surround with the optical cable. My primary DVD player doesn't even have 5.1 outputs... I'll admit I'm a little confused about all the different formats out there.

Thanks-