Controlling the audio of 2 Studio Displays

I'm currently using two Apple Studio Displays connected to my MacBook Pro. To play audio through both monitors, I've set up a Multi-Output Device in Audio MIDI Setup. However, I've run into a significant issue: I can't control the overall system volume using the keyboard volume controls with this setup.

I've tried third-party solutions like Background Music and SoundSource, but they haven't resolved the issue effectively. Is there a native macOS solution or workaround that I might be missing to achieve this functionality?

If no such solution exists, I strongly urge Apple to consider adding native keyboard volume control for Multi-Output Devices in a future macOS update. This feature is essential for productivity and ease of use.

Thanks for any help or advice you can offer!