Josh and I had this problem recently and he found the solution online. Here is the basics (I would post the link but you never know how long a webpage will be there.)
Basically you need to connect the SPDIF out from the motherboard or soundcard to the SPDIF in on the video card. The four images to the left show videocards with the SPDIF in in a red box.
The wire that you connect the pins with usually comes with the videocard, but if not, just use some spare wires that would lead to the LEDs on the front of the computer.
Now that you have connect the wires to the above mentioned connector on the videocard, you connect the other end to the SPDIF out on the motherboard or sound card. On the motherboard you need to find the manual or get it off line. It will tell you under the I/O (in/out) section of the manual. If you don't have an SPDIF out then you will need to buy an audio card, be sure it has an SPDIF out (2 pin) or is a high end Creative Labs card (look for the below connector, 10 pin).
on a soundcard, if it isn't labeled nor is it 2 pin, then try this. On Creative Labs cards it is a 5x2 pins connector with the last pin being the key pin. You want to connect in to the ones farthest from the key pin.1 2 3 4 5
6 7 8 9 K
connect it to 1 and 2
Now power up your system and go into your sound control and find the checkbox to enable digital I/O and enable it.If you don't do this, you will get no sound.
if there is no sound, flip one end of the connector wire so that the pairs of wires are reversed.
