Going by how my M22's sound vs. the original take 5's my brother-in-law had, I would say the M2's will be cleaner/crsiper sounding but as they will be for rear channel duty I doubt you would notice the differences enough to be bothersome.
Any reason why you are looking for inwalls as rear channels? How much distance do you have between the seating position and the rear channel positions, anything less than 4-6 ft and I would recommend getting QS series speakers. You need the extra depth for dispersion with the direct radiating style of speaker, otherwise it becomes very spot specific, then again that might be what you are looking for
