I have the in/on wall M22's using an in/on M2 center in a 7.1 setup with QS8's and EP500. I am very happy with the sound of the M22's and find they can play very loud, but my HT room is fairly small at something just under 1500 cf.
What size is your room?
From my experience when I built my HT, I was forced to consider only lower profile on-wall solutions, the Axiom in/on walls were the only ones I found that could deliver great sound quality at a reasonable price. Ask away with any in/on wall questions! I also found information specifically on the in/on walls tough to find, so happy to help.