Spence, as far as distance from the ceiling goes, even 2-3" should be adequate room for the top woofer. If you'll have back surround speakers in a 7.1 setup you don't have to have the side surrounds behind the seating position to give some "phantom" back surround imaging. The side surrounds should then ideally be directly to the side of the listeners or even slightly in front.

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Enjoy the music, not the equipment.