TO add to Chris' post, the M3's, at least in bookshelf form, have a slight lower midrange dip that gives them a slightly recessed/laid back sound, while the M22 bookshlef is more linear and the midrange clarity is excellent. I suspect this difference carries over to the in wall versions as well. I would use this as the guiding point between the M3/M22.
The VP 150 won't care too much about the vaulted ceiling but it will give you good clarity just as all Axiom speakers do. A vertical center will give you better off axis listening. This would be desirable if you have listening positions outside of your main listening area.
