Wow, quite the discussion I appear to have sparked.
I appreciate not all use cases are the same, but given the availability of things like, say Virtual Village - US | USB Mini Converter to SPDIF Output for $32, is that "good enough" to solve the problem at hand.
If jitter on the input S/PDIF is an issue, get something with a word clock input, and clock your audio bits, using the clock on your DAC. problem solved.
If your DAC uses ASRC, or reclocks the incoming bits, why are we having this conversation?
And why would you want your noisy, RMI/EMI emitting computer, within the maximum length of a usb cable, electrically coupled to your dac?
Just some thoughts to play with