Most of the details for the Atmos receivers say to put the audio input to PCM to let the receiver decode itself.
{I'm now with Anthem}
With even 5 or 7.1 and your Blueray set to the Atmos track it should still have more surround presence with just the audio select button. At least that was my opinion when still using 7.1 {Integra A.V.R.} the output of my Blueray players audio seemed a lot richer.
Around a couple months ago was trying to play Despicable Me 3 for my kids couldn't get the audio right for a couple days.
Turned out I had moved some stuff in my stand and unplugged my ADA's plugs from my receiver took a few tries to get them back in the correct slots with out pulling them out of the unit.
Have you checked your cables maybe something loose?
