How do I get surround sound from my pc to tv reciever?

-I have a nvidia gtx 480 and I'm running hdmi out of it with sound to my tv. And from my tv I have optic sound going from the optic out of the tv to the reciever. when I use other devices like my xbox or digital tv the surround works fine through just hdmi to my tv. I have windows 7 and I've tried changing the settings and I can only choose stereo and ive updated my nvidia driver to the latest.