Peter, although you refer to the "rear" speakers, apparently you're talking about the side surrounds which should be just slightly farther back than directly to the sides of the listening position. Your comment about the wall to the deck isn't entirely clear. Do you mean that there's no side wall position available for the mounting? If so, I'd think that a better idea than in-ceiling speakers would be to mount QS8s on the ceiling, spread widely apart and slightly behind the listening position.

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Enjoy the music, not the equipment.