I went on-wall instead. Just couldn't bring myself to put the holes in the ceiling, plus after some tests with my existing on-wall M3s, I noticed that sound coverage was noticeably better if the woofer could be angled, and not just the tweeter like the in-ceilings.

I need to get myself in-gear, get the wires run, and make some ceiling mounts at the correct angle for the speakers (front pair will be angled more than the "rear" pair.

Also, people are finally starting to publish information about best speaker locations for multiple rows of seats.

Dolby Atmos: Dispersion Requirements for Ceiling Speakers

Farewell - June 4, 2020