This is an interesting idea which I may pursue instead of using a laptop as a music server (the fan noise). NAD recently announces the little brother of the C390DD int amp called the D7050 which is also direct digital 50W (power DAC) and accepts wifi + all kinds of digital input while costing below $1000. Since it is direct digital then technically you can just use the PC directly USB asynchronous out which is jitter free to the integrated amp. This is I'm assuming that the only reason you use a USB to SPDIF convertor is due to the integrated amp's analog input.
http://www.audiostream.com/content/new-nad