Does that receiver have a digital coaxial input?
Digital out means the receiver will convert the signal to analog, not the soundcard. Unless you have one of those fancy M-Audios or Terratecs, the receiver's DACs are probably much better than the soundcard's output, especially if it's an integrated card or made by creative.
If so, plug the digital coaxial out of your soundcard into the receiver. Unless it's one of those Creative pieces of trash it'll send relatively the same thing a CD player would. It's
relatively cheap, incase your current soundcard doesn't have a digital out.
