For the Atmos channels, any of the two Crown amps mentioned as well as the Yamaha PX3 should be fine. If used in the front two channels, the M2200 would be my choice. They cost more, but didn't they say buy once cry once.
By the way, just noticed the PX3's specified 300/500 W output was for 20 ms burst, 1 kHz. That sound like just dynamic ratings, not continuous, though should still be good enough for the Atmos.