Can't help you on the questions, but you definately would not want to mount regular m80's in a wall that you describe, it would run the sound. The cabinet versions are intended to be mounted within a wall cavity, so that would be a better choice.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85