I was going to mount an FXi5 on the wall in my media room but my wife does not like it at all, i want to put an in wall speaker but there is not enough space in the wall. We want to build a box un the wall where the fxi5 would have been and put a TC65i in the box. since the TC65i is 12 3/4(h) x 7 1/4 (w) and requires 2 3/4 (d). what size enclosure (box) do we need to build to attach to the wall for the speaker without affecting the sound