How to extend the file types recognized by category in HKCR\SystemFileAssociations

Question

I have a similar question to the one that was asked here: Custom Windows context menu shell command targetting documents: *.docx and *.pdf except I am concerned with Audio file types.

I want to create a new context menu that is only visible on audio files.

Doing this on an extension-by-extension basis (which was the solution provided in the above question) is not suitable in my case because I need the added context menu to be visible when selecting multiple different audio types (i.e. different extensions, such as .wav, .mp3, .flac etc.). If the context menu is added on a per-extension basis then the menu will only be seen when homogenous files are selected. As soon as more than one audio file type is selected in Windows Explorer, then the context menu is no longer visible.

I can obviously get it to work by creating my new context menu key in HKCR\*, but this adds the context menu to every file type (so it appears on non-audio files where the context menu is not relevant).

Adding my new context menu to: HKCR\SystemFileAssociations\audio works exactly as hoped. My context menu shows up on .wav, .mp3, .wma, .aiff, .au, and some other audio file types, and it remains visible even when selecting across multiple different audio file types in Explorer.

However, the problem is that the audio file formats over which this works is limited. There are file types that I use all the time (such as .flac, .ogg and .opus etc.) that do not get the context menu added because they are not considered part of this 'audio' category of file types. I cannot work out where this list is being specified, nor how to add any new file types to that list. I do know that it's not down to PerceivedType though, because that was the first thing I checked.

Given that the extensions which are categorized as 'audio' all seem to have some kind of connection with Windows Media Player, I thought that creating similar associations and MIME Types for the new audio file types might work. But it didn't.

Does anyone know where this list is defined, or how to add to it? There seems to be a similar problem for SystemFileAssociations\image and SystemFileAssociations\document too (as mentioned by the OP in the post linked above). So it's not an audio specific thing; it's a general file-type Registry thing.