I don't think you're getting much in the way of a response because the room sounds like it's a really weak layout with speakers in rather poor positioning.
You are making some very serious compromises already, and moving away from a surface mounted speaker to an in-wall or in-ceiling speaker doesn't actually sound like it is an upgrade. The goal would be to get the speakers down to a proper listening level, in the proper position. I generally suggest, and hear, that the goal is to never use in-ceiling speakers. Instead, use surface mounted, floor standing, or bookshelves when possible, then in-wall speakers. In-ceiling is kind of a last resort and is rarely considered an 'upgrade'.
I use in-ceiling only in rooms where there is no rooms above it and when I'm just looking for an upgrade over the TV speakers (which they are).
Use the speakers which get you the best audio quality in the closest configuration to proper location for surround sound. If this is all about making the room look nice, consider ditching 5.1 in favor of 3.1 or even stereo so that you get better sound, not more sound.