Charles, I'm not sure what posts that you're referring to and I can't recall any discussion about using both a stereo and a multi-channel receiver in the same speaker setup. Of course using a stereo receiver in a stereo-only setup is fine, although an HT receiver wouldn't be out of the question. If you mean that they would be connected to the same speaker terminal, then yes, some type of switching device would be necessary to keep the two receivers electrically separated. There appears to be no good reason to do anything like this; a stereo receiver doesn't have any special advantage when only two speakers are playing.
