Sell the AirPods Max for as much as you can get and buy some headphones from outside the walled garden capable of Dolby Atmos from non-walled garden sources. Many of those will work just as well within the walled garden too while also granting you unlocked listening capabilities beyond what Apple Inc. chooses in a narrow range of use.
I do not think earphones have any impact on Atmos capabilities.
In case of AirPods,’magic happens inside iPhone or appleTV.
Atmos on blutay is in different format that appleTV can not decode. Plex will not help here.