Apple TV 4k - Audio switching to TV randomly from Receiver

Hi all,

I am really stuck with this issue and its making my new apple TV unusable for me if I can't fix it which would be a shame because I love its interoperability with all my apple devices at home.

So when I set the Apple TV up initially and run it into my Marantz receiver and then out from receiver to TV it will control the receiver and play surround sound through it. The apple remote will automatically control the volume through the receiver. This is great and how I want it to be except..... Upon restarting after the first setup, it reroutes the audio to the TV and no longer plays through the Marantz. I can only get it to work upon initial startup and not after putting it to sleep for first time.

Edited to add it switches from receiver via HDMI to TV via IR after initial setup and I can't get it back to receiver via HDMI

Anyone have any idea what the holdup could be here? Its driving me nuts.