Consider this a reply...
...from a disinterested third-party...I'm not fond of HT for any number of reasons, but...
In-ceiling speakers always smacked of Muzak-type sound...diffuse...omni-present and pervasive...Now if that's what your looking for with music...well OK, a nice sorta' bathed-in-sound kinda' deal is cool, but...I think for HT you are really gonna' wanna' have some directionality, particularly with the center channel...it can be psychologically disturbing to see an image at a fixed point and having disembodied voices, etc. come at you from, at best, another direction, at worst, no particular direction...it really is a symbiotic relationship...And with just music, you can say goodbye to any sort of soundstage, again that doesn't mean it can't be a pleasant experience, but it'll just sorta' be there...
Since you are in construction mode, have you considered in-wall units?
jimHJJ(...just my two cents, FWIW...)