Since you are connected by toslink and using an external decoder, you set your sound card properties to external digital decoder/pass through, right?
If so, your sound card shouldn't be touching it. It would be your receiver that is upconverting the 2 channel audio when you turn its dolby on. When you turn the Dolby off on the receiver, it should be the untouched 2 channel audio.
In order to hear audio over toslink on your friend's computer, you would of had to setup optical out somewhere, which would have told your sound card to output audio by the digital out. Maybe on his setup you set the external decoder/pass thru as with yours you didn't.
To answer question 2, I think that if your receiver is showing a 5.1 signal input when you play a non-AC3 source (music), then your sound card is touching it and you must have an option turned on to upconvert the audio source to 5.1 (do you use X-Fi with Dolby Live driver, by chance?) and you do not have the pass-thru option enabled.
These are all guesses, though, as I haven't had a receiver hooked up to my PC in awhile and don't have recent hands on.
If so, your sound card shouldn't be touching it. It would be your receiver that is upconverting the 2 channel audio when you turn its dolby on. When you turn the Dolby off on the receiver, it should be the untouched 2 channel audio.
In order to hear audio over toslink on your friend's computer, you would of had to setup optical out somewhere, which would have told your sound card to output audio by the digital out. Maybe on his setup you set the external decoder/pass thru as with yours you didn't.
To answer question 2, I think that if your receiver is showing a 5.1 signal input when you play a non-AC3 source (music), then your sound card is touching it and you must have an option turned on to upconvert the audio source to 5.1 (do you use X-Fi with Dolby Live driver, by chance?) and you do not have the pass-thru option enabled.
These are all guesses, though, as I haven't had a receiver hooked up to my PC in awhile and don't have recent hands on.
