^+1
Of course, there are crappy cheap DACs with asynch USB, in which case a good DAC with coax input can sound superior as long as the jitter is controlled with a reclocker gadget between the source and the DAC.
iFi iPurifier (original version is SPDIF, 60pS jitter - $110)
Empirical Synchro-Mesh (20pS jitter - $600)
There are also USB decrapifiers (see other thread) to further clean up the USB signal, even for async USB DACs.