Originally Posted by InternetSandman
I'd prefer S/PDIF, I've heard USB isn't quite as refined and requires drivers to get the highest resolution audio files through to the DAC. If USB provides equivalent sound quality to S/PDIF then this entire topic is moot, but given what I've gleaned so far in my research this doesn't seem to be the case
I wonder what your sources are. Moon audio reviews?
To convert digital data stream to analog audio signal, your DAC needs three things: the data itself, the clock signal, and of course power. Data stream is always the same, whichever way it gets there. Power source is also the same if we're talking about a unit that supports both USB and S/PDIF. Out of the three only the clock is really different, and here I'd say that USB should have an edge, as it uses clock on the DAC side - these tend to be more precise than what your typical motherboard provides.
USB is more prone to buffer underruns (which manifest themselves as gaps and clicks), but this is usually caused by poorly configured systems. It is also a bit more difficult (and costly) to implement, so some manufacturers claim it's inferiority just to make sure they can sell their S/PDIF-only gear.
My advice is not to stress too much over the interface: on good gear you won't hear any difference. Just use what is most convenient.