Why not use an AT screen? I'd be hesitant to use an in-wall center speaker, as it can't be tilted up towards ear level and must be able to fit between 16" OC studs, necessitating vertical orientation. Either the speaker will end up near the ground, or the screen will have to be placed too high. Will your walls allow 6" deep speakers, or do you need 4" deep speakers?
You have the room depth to do a false wall with an AT screen and regular LCR speakers and subs hidden behind the false wall. Check out the dedicated theater subforum, people's build threads, etc. For a dedicated room I'd want to leave budgetary space for acoustic treatments, even at the expense of a lower speaker budget.
For what it's worth, I like Triad in-wall speakers a lot, and I use their in-ceiling Bronze LCRs for a living room surround setup. They are awesome products at their price point. In your setting (if you could use and AT screen) I'd go with Triad Silver/4 In-wall LCRs and Bronze/4 In-wall Surrounds. I'd buy the subs elsewhere to get more bang for the buck. If you have more budgetary room and 6" wall depth, you could go with Gold/6 LCRs and Silver or Gold surrounds.