I know only that: the library files on Mac OS are located inside the "AnimeStudio.app". An .app on Mac OS is a directory only. And inside that directory you find the library files.
It works for me. Your custom elements end up in your assigned folder (generally in "documents"), native elements are found in the package in your application folder ("Show package").
It launches for me within anime studio, however there is tiny a bug I feel. Anytime I save something into my content library, I have to be very careful that no folders are expanded or else the element will find itself in some totally random other element folder instead of the top level.