USB to S/PDIF converters

Strongly recommend you look for boards using the SA9227 chip. It has the advantage of supporting three oscillators. One fir USB, and seperate ones for 44.1kHz and 48kHz based frequency audio. Handles all the way up to 384kHz with ease, and if you get a board with three oscillators on it, you can switch out the cheap oscillators that Chinese manufacturers use for high quality low jitter oscillators from SiTime or other good makes.
I use the SA9227 chip heavily in my own designs and it's excellent!