I think some others will reply, but I'm afraid your not going to have very much seperation between the two m80's, or 60's for that matter if you hide them in that small opening. Besides you need some beathing room behind the speakers to let the Low Bass frequencies to filter into the room, my guess is they will not give you the same experience as in a normal setting. You might want to consider the Architectural OnWall/InWall series like the W22's, since your going to have a Sub for the lows. I believe Axiom recommends around 8ft+ for the M80's for seperation. I have my M60's about 13ft apart.
