It comes out of the sound card or the motherboard if it has integrated sound.
And more than likely the sound is stereo and not surround. Actually all you need is an audio cable from line-out on the sound card to the sound system. Just check the connections on the computer and the sound system and get the proper cable accordingly. Post back if more info is needed. Good luck.
More specifically through the surround sound connected to the TV. I ordered a vga cable from monoprice.com that I thought would enable me to do this task. I was hoping it would connect from my TV to the PC, but one of the ends in the cable was the wrong one. I have to return it. Can somebody give me the right equipment I need to do this? My TV has HDMI, DVI, VGA, Component, and much more. I obviously also have a stereo/surround sound system.