Dolby Atmos pass through from iPhone 15 Pro over HDMI

I'm already playing Dolby Atmos tracks from Apple Music on my Denon AVR-X3700H Receiver. My iPhone 15 Pro is connected to the AVR via HDMI and Apple USB-C HDMI dongle. iPhone indicates Atmos version of the track is playing.

Yet it seems only 5.1 PCM sound is coming to the receiver, not the original Atmos signal. The receiver shows "Multi-Channel In" as the source. When I play titles from my Linux box with Atmos the receiver actually shows "Atmos" and there is a huge increase in quality to "Multi-Channel In".

Is there a way to set up the iPhone 15 Pro to do a pass through of the Atmos signal to the AVR Receiver over HDMI?