There's been quite a bit of discussion on the board touching on this area. You might do a one year search using "horizontal"(and)"M22" and "M22"(and)"center". Note especially Alan 3/20 and Ian 3/30 on HT.

My own preference isn't horizontal orientation at all, but rather a vertical M2 if Axiom speakers are involved.

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Enjoy the music, not the equipment.