I certainly am no expert, just recently getting back into it... however from the research I have been doing it appears to be more the media player... for example McIntosh recommends JRivers... which if I understand correctly sends the signal directly out the USB through the McIntosh drivers. Therefore the the audio portion of the OS audio kernel is by passed and should have very little influence on what you hear.
The USB signal is therefore sent directly into the DAC which the cable is attached (in my case the one inside the McIntosh amp)... Always better sound not going through the digital to analogue convert within the computer (audio kernel).
I thought that the moment you connect an external DAC to any computer, then that is the one doing the conversion, so the operating system should not have any influence, but indeed please correct me if I am wrong.