What you want IINA to do:

It would be awesome if IINA could passthrough surround / Dolby Atmos streams to connected AirPods so they can make use of the new spatial audio features in macOS Monterey.

What IINA does currently:

Currently, IINA downsamples surround streams to stereo when connected to AirPods.

Why you think this should be added:

It would enhance the movie watching experience.

Examples of other projects that have something similar:

Since this is a fairly new feature, I've only seen QuickTime, Safari, and their TV app support this so far.