What centre channel are you using?
What's your listening distance?
What's your room layout?
What subwoofer(s) are you using?
What is the TOTAL volume of your room (open-concept, dedicated room, etc)?
What is your budget?
You will probably get suggestions from budget Polk in-ceiling speakers to speakers that might rival your mains. Whatever speakers you choose, there are a few things to think about
1. Sound leakage. Many in-ceiling speakers don't have a backer box, and that can cause sound to leak into the room above. If this is an attic, then there are no worries. If it's a bedroom, then there could be some issues.
2. Dispersion. One thing that the Dolby specs don't mention is that for a true Atmos experience, all seats, especially the MLP, should be within the radiating pattern of ALL Atmos speakers. It makes no sense to spend a lot of money (or any money) on speakers that you can't hear. I suggest in-ceiling speakers with an angled baffle, or at least aim-able tweeters, that can be aimed at the MLP. The RSL C34E in-ceiling speakers have a 15-degree angled baffle that many on her have used with great success: https://rslspeakers.com/c34e-ceiling-speaker/
3. It may sound like blasphemy, but your Atmos speakers do not have to be the same make as your mains. The AM1 speakers are actually a very good suggestion, if B&W's specs can be believed: (-6dB at 46Hz "wall mounted"). It's an outdoor speaker with a mounting bracket that will allow you to aim them wherever you want. $700/pr
CAD is a bit steep for my tastes, but it's your decision.