tvOS 27: Loss of Surround Sound/Dolby Atmos on Apple Music with AV Receiver

Device and Software:

• Device: Apple TV 4K
• Software: tvOS 27
• Audio Equipment: Yamaha RX-475 AV Receiver

Explanation of the Issue: Since updating my Apple TV to tvOS 27, Spatial Audio/Dolby Atmos tracks on Apple Music are only playing in stereo on my AV receiver. On tvOS 26, the Apple TV correctly sent a surround sound signal.

Steps to Reproduce:

1. Connect the Apple TV 4K to a Yamaha RX-475 receiver via HDMI.
2. Set the Apple TV Audio Format to "Auto."
3. Set the Yamaha receiver to "Straight" mode (to ensure no artificial DSP effects are applied).
4. Play a Spatial Audio/Dolby Atmos album on Apple Music.

Expected Result: The receiver should play the audio in surround sound, as it did on tvOS 26.

Actual Result: The receiver plays the audio in stereo. Because the receiver is set to "Straight," it confirms the Apple TV is only outputting a stereo signal, rather than down-mixing on the receiver side.