Continuing the conversation on in-wall.
Also requested by Mrs to build in wall speakers (for the office).
Assuming X-Ls encore drives, the idea would be to produce a 2.1 or 3.1 system. The sub (probably an x-sub) would be outboard, under the desk.
Would it help if the inwall box was thick steel, aluminum or perhaps carbon fibre composite? Assuming it was rigidly attached to the studs I would expect it would not resonate any worse than wood, and allow the whole 14.5x3.75 inch column, or is that an incorrect? Of course the drivers would mount on a wood panel which would be screwed onto captive nuts in the steel part.