Welcome SD. I have the in/on wall version of the M22s and VP150. I have no specific issue with sound proofing (bleed through) of these speakers, although I did build and mount them in a 2x6 wall instead of a 2x4 wall and have a layer of safe n sound insulation behind them. That was done as part of my overall soundproofing of the theater room and not specifically for the in/on wall design. I will say that in a standard 2x4 wall construction you won't have room for much insulation behind them in wall installation. However as long as the back of the cabinet is not in direct contact with the drywall on the opposite side I don't think this will be an issue beyond general sound proofing of your HT room.
Cheers,
