Ok I have the same sound card and the same set up as you want so I can explain better.
Ok there is a couple ways to do this. The way I have it is on the front panel of my soundcard I hook up a coax cable(can get at radio shack for cheap) to the SPDIF OUT port. I then plug the other end of my coax cable into the coax IN port of my receiver. Turn your receiver to your Coax channel and your homefree.
You could also get a cable from that looks just like your speakers cables(instead of center,left,right,sub, you have one cable that plugs into the digital OUT)plug it into the digital OUT port and into your receiver.
If you have anymore question feel free to ask me.