Are there any inherent advantages to handing off audio to the dac via USB?Asynchronous USB has the same advantage as Ethernet or Wi-Fi - making internal DAC clock completely independent from computer clock. In contrast S/Pdif transmission is prone to jitter, that DAC has to reduce, either by syncing (PLL) internal clock to average S/Pdif clock, or by use of asynchronous rate converter (my Benchmark DAC).
Ethernet seems to be the obvious solution for digital audio, but for some reason it is less popular than USB.