Hello,I'm just wondering about how different the AQ from digital stereo sources would be?
I think the XDA-1 would indeed be superior in that it is a Differential DAC and roughly costs the same as the UMC-1. Much of how different they sound will come down to your Associated Components. Namely your Speakers.
The UMC-1 has gotten excellent Reviews for how it handles 2 Channel, but the XDA-1 is a whole different beast entirely.