Some terminology:
The sections, Audio, Video, Images, etc, are Views. More specifically, they are View containers, with one or more views inside of each one. Like Audio normally has Albums, Artists, etc.
You can turn on and off some of these from the Options settings, but I think you probably deleted Audio altogether because it's not one of the ones you can disable. You could rebuild it manually, but that's kind of a pain if this is just for "documentation" (like to show screen shots and things).
Instead, we can build you a brand new library and it should have all of the default Views, including a fully populated Audio view. I would recommend that you play around with this new library and do your documentation with it. Then when you're done, I'd probably delete the new library. That way it's less confusing. Most people only need one JRiver library.
To make a new Library:
File > Library >Library Manager > Add Library ...
Then you can switch between Libraries with File > Library > (select from list of Libraries)
Finally, you can delete your temporary Library with File > Library > Library Manager > Delete Library
Note that your new library won't have any media files imported into it. Because it's brand new. You can import whatever files you want to show in this new library.
Good luck.
Brian.