So here's my pickle.  I am currently running my Apple Airport Express through my DAC1 using the AE's optical out.  However, if I wanted to use a USB DAC, I would need a converter for the SPDIF--->USB conversion, correct?  I'm aware that such things exist, but I'm wondering: 
 
a) Do they actually work well in practice, and 
 Would such a converter work coming off the AE instead of directly out of a PC?  In other words, most of the converters I have come across tend to have a PC in the mix, which indicates to me that maybe there's a driver issue.  But I don't know shit, so help me out.