Re: Help putting playback system together, please.
About the same response I posted elsewhere but before getting too far into how to get a 3.1 signal into your system you may want to first verify that the existing installed speaker system can properly support a 3.1 signal.
I don't think the analog mixers you apparently used prior to getting the Pro1 supported actual LCR operation and since those are what were being used when the speaker system was installed then it seems unlikely for the system to have been designed and/or programmed as a LCR system, it seems more likely to be stereo plus center mono or even straight mono. Similar for the .1 LFE channel of 5.1 or 3.1 as the installed speaker system would need to be configured for a dedicated LFE or subwoofer input channel and unless you were running aux fed subs then the system may not be setup to work with a dedicated LFE/subwoofer signal.
My understanding is that S/PDIF can carry two channels of PCM audio or multi-channel compressed audio, such as encoded surround going to a surround sound decoder, but I do not believe that a S/PDIF audio stream can carry four discrete channels of decoded audio as you seem to be wanting.
