If you connected the HDMI directly to the TV then all you will get is 2.0 sound. Most TV's do not send 5.1 out. For example if I connect the HDMI from my GTX 670 to the TV it will still send a single to my receiver though HDMI but it will be only 2.0. However connecting the HDMI to my receiver then the receiver to the TV I will get full 5.1 DD TrueHD and DTS-MA. So in short to get 5.1 you HAVE to connect the PC to the receiver. If your receiver does not have HDMI in you could connect the optical from the PC to the receiver and that should let you get DD and DTS but as I understand it you would not get 5.1 PCM because of the limitations of optical.