@David-Healey I'm still not 100% sure why the need to install to both system and user spaces on Mac. Can you explain?
As far as I understand, it's to install the plugin to the system /Library folder (for all users) and the samples to the user ~/Library folder (for the current user only).
What's the point of installing the plugin to the system folder for all users if the samples are sandboxed to a specific user? Other users on the machine won't be able to use the plugin without the samples.
The only reason I can think of is that DAWs have the system plugin folders set as default (/Library/Audio/Plug-Ins) but not the user plugin folders (~/Library/Audio/Plug-Ins).
Meaning some DAWs might miss plugins installed to the user Plug-Ins folder unless the user updates the search paths.
I don't know for sure what plugin paths DAWs use by default. Would be a good one to look up.