If you had not said in-wall or on-wall, I would have said M22 L/R and phantom center if MLP is not off center and if your receiver supports it. I have M22 bookshelf speakers in a much larger room. I have the VP150 center (upgraded from VP100) only because we have a wide viewing area. I would run a phantom center but we have multiple viewing positions. If I were buying a center today it would be the VP160.
I don't know how the in-wall or on-wall compare to the bookshelf speaker. The M22 bookshelf is an outstanding value with excellent clarity for any 5.1 system. I would not suggest the M3 for clarity and the M2 may not drive your room size.
So for me it would be M22 L/R and either a VP160 or a phantom center depending on viewing positions.
