My experiences with inwalls are that the sound is going to be way compromised, so why get picky? No matter what you use, the sound isn't going to be supper stellar.
I would suggest looking into some of the horn loaded inwall designs myself. Klipsch probably makes some. You'll need an EQ for his system, as there's no other way to get around the boomy/peaky sound that's going to happen with inwalls. The inwall location excites all the room modes, and makes for an uneven sounding pressentation. The inwall situation is already a sonic compromise, so you'll need to try to make up for this with the EQ.
good luck
I would suggest looking into some of the horn loaded inwall designs myself. Klipsch probably makes some. You'll need an EQ for his system, as there's no other way to get around the boomy/peaky sound that's going to happen with inwalls. The inwall location excites all the room modes, and makes for an uneven sounding pressentation. The inwall situation is already a sonic compromise, so you'll need to try to make up for this with the EQ.
good luck