MM, I assume that you're using the QS4s as side surrounds in a 5.1 setup, not back surrounds in a 7.1. In that case they shouldn't be "directly behind" the couch. Since they can't be on the side walls they should be on the back wall possibly 5-6' up and separated as widely as possible, so that even though they're on the back wall, some side surround effect is given.

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Enjoy the music, not the equipment.