Mata, for 7.1 it'd be best to use the QS8s for the side surrounds, placing them on or near the sidewalls, preferably 2-3' above ear level and directly to the side of the listening position. The E10s could be used for the back surrounds on or near the back wall and at the same height as the QS8s, separated by about as much as the listening position is in front of them.

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Enjoy the music, not the equipment.