Outputing surround sound from mini displayport while in bootcamp

I occationally boot up my macbook pro into bootcamp to run windows. I hook up my computer to my tv and surround sound system through the mini-displayport. When I am in mac-mode, i can actually output surround sound to the speakers, but when im in windows, i can only output stereo. I've tried to configure it through Control Panel>Sound, but it only lets me select Stereo as the mode. Does anyone know if there is an additional driver that will allow this? Thanks