Well, Atmos adds significant complexity to the accurate reproduction of an audio mix because it has so many additional variables to control for.

However, you’re in luck. The center channel is reserved almost exclusively for the dialogue track in film and TV, so you should be able to turn it up and hear it more clearly without affecting anything else.

> and little to nothing that is done either on the receiver, ATV, or playback source

Well of course, it's nothing indeed -- they're simply passing through the audio as it was originally mastered, as they're meant to.

All your equipment is doing it right, assuming it's all configured correctly. And I assume it's not that the Roku "doesn't do much better", but does it exactly and precisely the same.

If you have an issue, it's presumably with the mastering standards, not with any of your equipment. Which is a whole other conversation around relative decibel levels in mixing, but it has nothing to do with technology.