Shao128

I had a whole reply typed out but it seems to have disappeared, strange, anyways I'll try and recall what I said. To get 5.1 sound over spdif (Dolby Digital / DTS) you need to enable exclusive mode on your sound card. Outputting 5.1 sound requires exclusive access for the application outputting the sound. Any other application that tries to produce sound while another application is in exlcusive mode will be denied. 5.1 audio cannot be mixed, it 1 stream only. So to get 5.1 sound you will need something like ac3filter to do the passthrough. PCM audio is 2 channel and can be mixed which is why you only see the stereo option in control panel from your screen shot. Also when you use spdif passthrough (5.1) you will not be able to control the volume through your PC, the receiver will have to do that.

If the content you are playing is only 2 channel you are better off setting your receiver to virtual surround (every receiver calls it something different) and have it simulate 5.1