It is best to not substitute surround speakers with in-ceiling. But, for the atmos height channels themselves, many forum members here will be in high praise of in-ceiling speakers. But, before you start cutting holes in your ceiling, watch this video from a really smart guy who knows a whole lot more about this stuff than anyone around here. He makes a very key point in this video.
I am one of those guys who listened very carefully to the smart guy on this video, took his advice and went with upfiring atmos modules for my current atmos setup and limited basement flat ceiling height of 9 ft. I will add 4 height speakers for Auro when i am Auro enabled in the future and device a solution to easily switch back and forth between upfirng modules to height speakers (but, i have nixed the in-ceiling speaker route, not for me).
Watch the impending fireworks on its way from the ceiling hole gophers on this thread now

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