Very good, Dean; that's certainly quite a bit for just "preliminary tests"! Not my favorite configuration, but one other that you might check would be vertical M22 centers immediately at the left and right edges of the screen.

On using the QS8s as back surrounds, of course you can apply DPLIIx to both 2 and 5 channel source materials to give the back surrounds some work.

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Enjoy the music, not the equipment.