Despite blabbing at length I realize I forgot a couple points. Even though you have a tough room, the better AVRs have decent room correction built in that will help you deal with that. I’d say Anthem has a leg up on others with their proprietary ARC room correction, but that needs to be reconciled with your budget.
For your center channel, I’m not a fan of in-wall if you can accommodate an in-room center, but if ya gotta ya gotta. I can’t speak to B&W in-wall speakers, and despite not being a huge B&W fan myself I do very much like their center speakers and would find it hard not to pair the 804s with the HTM2 D3 (I’d suggest going with cheaper surround speakers to get the best center you can as the center is absolutely critical to fully enjoying the HT experience IMHO). The HTM71 S2 might be a workable alternative if the D3 isn’t in the budget, but I’d consider it a distant second. Anyway, FWIW.
For your center channel, I’m not a fan of in-wall if you can accommodate an in-room center, but if ya gotta ya gotta. I can’t speak to B&W in-wall speakers, and despite not being a huge B&W fan myself I do very much like their center speakers and would find it hard not to pair the 804s with the HTM2 D3 (I’d suggest going with cheaper surround speakers to get the best center you can as the center is absolutely critical to fully enjoying the HT experience IMHO). The HTM71 S2 might be a workable alternative if the D3 isn’t in the budget, but I’d consider it a distant second. Anyway, FWIW.