If you've got a digital output on the soundcard/motherboard, just hook it up (just like hooking up a DVD player's audio). Digital makes even on-board audio sound good. There are two types of digital audio connection: Coax, and optical. Your receiver must support the type of output the motherboard supplies; any halfway decent receiver supports both. If it's coax, you should use a 75 ohm composite video/digital audio cable, but a regular RCA cord (like the one that came with your CD player, for example--or rather, just the red or white half of the RCA cord) will work just fine if the length is short. If it's optical, you'll need to buy an optical cable.