I would try it with the onboard sound, maybe. You have 8-channel and both optical and coaxial SPDIF outputs. One thing, though--what do you mean by "5.1 surround sound system"? If it's a dedicated speaker setup like Logitech's
(don't get me wrong, I am NOT recommending that), you're in business. If you mean SPDIF to a receiver setup, then to get surround sound from games you'll need a sound card with Dolby Digital Live or DTS Direct. Unless your video card and receiver both do audio through the HDMI, and you're running Vista or 7 (I think). Also unless your receiver has discrete analog inputs for each of the 6 or 8 audio channels.