Your opinion on best In-Wall Speakers for HT Use?

I am building a relatively high end Home Theater system based on a Lexicon MC12B and a Lexicon LX-5, five channel amplifier, for the rear 4 speakers. (FWIW, front amp is a Theta Dreadnaught and front speakers are undecided, but probably Vandersteen)

I am forced to use in-wall speakers (not wall mount, but actual in-wall) for all 4 rear channels, 2 speakers to be placed on side walls and 2 speakers to be mounted to ceiling, obviously firing downward. From your expereince, what are the best in-wall's for my use? I am considering Thiel PowerPoints but at $5,000 for all 4 speakers, that is a bit much but I am open to your ideas and opinions. Thanks in advance for your advice.