Robb, it's unclear why your center speaker would have to be recessed rather than being at the front edge of the rack. No, it wouldn't make a "huge" difference, but the diffraction should be avoided if at all possible. My suggestion would be to consider a third M22 positioned vertically under the screen as the center and to rearrange the rack to the extent necessary to provide the room.

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Enjoy the music, not the equipment.