I'm thinking of going down the same road with in-walls though I have just begun my research on who's doing what how.
I keep seeing an issue with the back enclosures and sound quality with in-wall speakers. My question is if you are modifying an exisitng wall, as in my case, why wouldn't you buy cabinet speakers for LCR, fabricate mounting platforms for them behind the wall, (I would be able to do this as I'm using the wall of a pre-existing walk-in closet), take the screen off the front of the speakers and cutout/mount a screen on the wall in front of the speakers?
Just one of the options I'm looking at. Any advice much appreciated.