Interesting - I noticed a tonal shift over the weekend when doing a little maintenance tweaking using a pink noise signal. The left M60 sounded different than the right M60. The left speaker is about 1.5 feet from the left wall and abotu a foot from the subwoofer, whereas the right speaker is butted up next to a chaise lounge that partially covers the lowest woofer - there is no wall on the right side. The tonal shift was minimal, but noticeable nonetheless. Obviously, the pan from left to right, through the VP100 mounted at mid-m60 level exhibits some shift as well, but when playing "real" material, I don't notice any difference between the left and right speakers at all.
To add to the original poster's question - I think the In-wall speakers would be a great addition to a 7.1 system. The low profile means that the couch doesn't have to be as far from the back wall to get optimal performance. The downside, of course, is that you really can't aim the speakers by using a wall mount, like you coudl if using a direct firing M2 and the FMB.
