Your receiver probably has digital coaxial and/or digital toslink cables.
Depending on your sound card outputs, you will need a different cable.
If your sound card has toslink output, and your receiver as well, you need a toslink cable.
If your sound card has a mono RCA (digital coaxial) output, then you need a mono RCA (digital coaxial) cable.
If your sound card is a Creative sound card and only has a 3.5mm stereo mini out for the digital output, then you need a 3.5mm stereo mini to RCA (or mono) cable from Radio Shack. If you get the -to RCA variant, you would use the white (mono) rather than the red end to your receiver.