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In-Ceiling and In-Wall speakers are something we talked about a lot but they are not coming in the near future.
So going with alternatives like our 1961 Heights is a great idea.
If you absolutely have to have In-Wall or In-Ceiling speakers, something that has a balanced/neutral sound, with good on and off-axis response will work just fine. It also should fulfill your SPL needs of course.
You will still need to equalize the sound to match it to the rest of the system.