Can't tell you about the in-ceiling M3 but I recently set up a 5.2.2 (Dolby enabled front) in a small-medium room/10 foot ceiling with an Onkyo 636 and The Expendables 3 was amazing in Dolby Atmos. The new Dolby Surround feature that comes with Atmos receivers was quite impressive as well (crowd noise) when watching the football game.
That's great to hear as I'm looking at a 5.2.2 as well. So even if the track isn't recorded in Atmos, the Dolby mix is still worth it? Nice!
Coming from an individual that never liked Dolby Pro Logic II (which Dolby Surround replaces) and other up-mixers, I am finding Dolby Surround can be a VERY useful feature that can definitely make improvements to soundtracks in your current collection.
Even with little Atmos content at the moment, Dolby Surround will put in-ceiling speakers to good use.
