Sure, Mike; this would especially be the case if at that particular moment the center channel material that would have to be played by the M22s was louder than what the M80s and other speakers were playing at the time(hope that you had some ears left afterward). So, at least three factors come to mind: possibly louder material, slightly less sensitive speakers, and possibly even lower net impedance at the frequency in question with the center speakers being run in parallel.

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Enjoy the music, not the equipment.