Apple Music spatial audio will not output 7.1 on Windows

Despite trying with multiple 8-channel (7.1) audio devices on Windows, Apple Music's spatial audio will not output 7.1. It caps it at 5.1.

The audio interface I am using (RME Digiface Dante) has its own WDM device configuration (MADIface) which allows you to configure 8-channel multichannel audio output devices that are selectable as playback devices in Windows. I have tried configuring them as a digital receiver and as a speaker. Windows is able to select both, and sends test signal to each of the 8 channels correctly. Within the Windows sound settings, I've also tried setting them both with and without ability for apps to have exclusive control. Still, despite configuring it every-which-way, Apple Music will not output higher than 5.1 to this audio playback device.

I even tried using a virtual cable app, Voicemeeter. It uses an 8-channel virtual audio input that is selectable as a playback device in Windows. In the app, you can then route the input to any audio output your machine has, including ASIO drivers. Similarly, it works with Windows, sending test signal to all 8 channels correctly. But Apple Music still will not output higher than 5.1 with this selected as the audio playback device.

I am using a Windows 10 machine, and Apple Music 1.6.4.90.