Hello @Luke23 ,
In the device setup screen for the HDMI output, make sure you have “Exclusive Mode enabled” and Channel Layout set to “2.0”. This should send a two channel stream to your Denon allowing it to use it’s own processing.
The reason for this option is that some receivers will malfunction when not sent a multi-channel stream. It’s a fallback to allow Roon to play to these devices.
-John