If you look around, there are several discussions of this, using some parts from audio_gd if I recall correctly. I think one person got it working, but I think they had lots of problems making everything work correctly. I had better success using the digi+pro over coax, as I thought the USB sounded really tinny and "off." I was going to build a silent home theater PC, but instead opted for the PS Audio LanRover, which is expensive, but requires no work (as compared to building and maintaining yet another PC) and sounds amazing. It also allows me to use the household wired network, so the noisy computer is far away from the stereo setup. Still way cheaper and more powerful than any of the proprietary component pieces, and can use JRiver to access SACD iso files, which is very important.
Good luck!