I recently got a new HDTV and I wanted to hook up my Xbox properly, but the only inexpensive HD output cable I could find had an optical TOSLINK audio output instead of the SPDIF Coax that I needed to hook into my sound system. It also had standard stereo left and right, but wanting the best output I could get. I wanted digital audio out.
After a little research, I discovered that the signals for TOSLINK and SPDIF are pretty much the same, and I ran across this site: http://wrongcrowd.com/staticpages/index.php/xboxspdif .
HAH! I have you now! A quick dig in my electronics inventory came up with a female RCA jack. A couple bits of wire and some solder later I have my Xbox hooked up with full digital sound.