Atmos audio will not stream from Apple TV 4K

I am unable to play Dolby Atmos audio from my Apple TV 4K. It will stream 4K and Dolby Vision, but Atmos audio streamed from Netflix will not work.

I have an LG C7 smart TV, and an Xbox One X, which can both stream Dolby Vision and Dolby Atmos content from Netflix to my Yamaha RX-V683.

I have followed the instructions from Apple support to configure my Apple TV to stream Atmos audio, and the Apple TV does report ‘Atmos Available’ under Video and Audio > Audio Format. When I select Atmos content in Netflix, however, it reports 5.1 audio available, not Atmos. The 5.1 audio streamed is also noticeably different from the Atmos audio delivered to my other devices.

1. The receiver has the latest firmware, as does my TV, and both of my other devices can successfully stream Atmos audio to the receiver over HDMI.

2. All of my devices are using high-speed Belkin HDMI cables.

3. My Apple TV is running the latest software (TVOS 12.1) and the Netflix app is up to date.

Is there an issue with compatibility with certain AV receivers like the Yamaha RX-V683?