How to Use The SPDIF Connector Available on GeForce Video Cards
 

The purpose of this small connector is very simple: it is used to allow digital audio to be routed to the HDMI output. All video cards have one or two DVI connectors, and any DVI connector can be converted into an HDMI connector by the use of a simple adapter. The problem is that the DVI connector does not transmit audio signals, only video, while HDMI can transmit both audio and video.

So if you convert a DVI connector into HDMI to connect your video card to your HDTV, you will only get video on your TV. The audio must be transmitted using a different way. The most common way to connect your PC to an HDTV is to convert the DVI connector into an HDMI and then use your analog PC speakers to get the audio or connect your PC to your home theater receiver thru an SPDIF cable, getting audio from your home theater speakers. In other words you will need at least two cables, one connecting the video (DVI-to-HDMI) and another connecting the audio

http://www.hardwaresecrets.com/article/600