If you buy in-walls and don't want the sound to transfer to adjacent rooms, just make sure that the speaker is completely enclosed. All Triad In-Walls have enclosed cabinets.
Keep in mind, that Triad speakers within a series (Bronze, Silver, Gold etc) are designed to sound the same -- cabinet characteristics, driver placement, and crossovers are all adjusted to make each speaker sonically identical. So, for example, InRoom, InWall, OnWall, and even InCeiling speakers should match one another acoustically.