Here are the only two links i found in regards to ML in walls.
I am considering a set of the Voyage in walls for my main and a passage for the center and 2 rear speakers.
I listened to the passage speakers briefly at a local store but they were a demo unit the the ML rep left them. The small room and the setup they had them in showed that they truly do have a sweet spot. But overall they sounded good for the mids and upper, but definately lacked the low end for jsut listening to music.
I havent been able to listen to the Voyage set, and maybe with 2 8" drivers instead of the 6 1/2" of the passage they would probably be a better match for my main speakers. However at $2k a pop that is a big jump from the $750 of the passage. For $4k I bet i could get a much better speaker than than the voyage in a free standing model.