I have a Asus p5q pro turbo with an onboard optical audio out (toslink connector) , running windows 7, all drivers are up to date. 

There is an audio distribution system in my house, with input panels in different rooms in the house, with optical in (toslink) ports. 

I tried plugging my PC into the audio distribution systems optical port, but , no audio. 

So, tried plugging the PC into an normal a/v receiver, and pc audio outputs just fine via the a/v receiver. 

Plugged my sony ps/2 into the audio distribution system via the ps/2 optical out, and, it worked perfectly. 

So, I know the PC optical out port is OK (ok via the a/v receiver), the audio distribution system optical in is OK (eg, from the ps/2), but, there is no way I can get the PC to output to the audio distribution system. 

I've tried updating to different drivers, (from both motherboard/sound chip companies), tried changing the playback settings (you can set the audio in the Playback devices/properties), but cannot get it to work. 

My theory, is that I need to output 2 channel sound , but the desktop will only output dolby format. But, there must be some way?

Any ideas?