Let me add a coupe of thoughts. For one of my setups I have an older JVC receiver, and in spite of bringing the audio in on a toslink cable and having the source (TV in this case) sending all 5.1 channels (can't really verify), any of the surround modes just don't work even though I have left, center, right speakers hooked up. It seemed like it worked before but doesn't now, but with any surround mode the sound is way messed up, so the center channel speaker is basically a riser for the TV now.
The other setups have newer Yamaha receivers and those work fine but I generally don't enable the DSP modes, except for 7ch Stereo for some things (radio mostly).
Chris