Dan92075,
Galvanic isolation on the USB input of your DAC is good thing to have, however, it is by far not enough to receive clean signal into your DAC. This is because the data stream your DAC get is already "spoiled" by one ot another degree by the quality of the power supplies supporting your server. Also, as Ryan Mintz of Core Audio correctly noted above, the DC:DC convertors, as a rule, degrade substantially improvments produced by high quality power supply. Thus, handling of electrical signal is paramount in music servers, and we at Musica Pristina pay enpurmous attention to it.
I would add that high quality software environment plays equally important role in resulitng sound quality but its the outside the scope of this discussion.
All The Best,
Simon Thacher
Musica Pristina