The way M3c attach to the ceiling is more than adequate, the wall board has no problem holding them.

That said the M3c is a big compromise and bit of a disappointment sound wise. I may write more on my findings as I'm still evaluating them in different spaces, experimenting with augmenting them with subs, and will try to see if equalization can improve anything.

They may fair better in a ATMOS setup since the low-end is where they fall short.