Re: 5.1 Not Working

This is not how mixing 5.1 works at all, in any application. A Toslink cable and a regular AV receiver won't do anything. It will pass a digital stereo signal to your receiver and that's it (or, in case of DVDs, an encoded DD/DTS surround stream but all that has nothing to do with mixing surround).
You need a proper multichannel audio interface such as a Fireface from RME or M-Audio. You then need a receiver that has discreet outputs for each channel or active speakers that hook up to the interface. Then each channel needs to be assigned to the proper interface output/speaker.

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