I think you have some confusion going on here. There are two *separate* concepts here. 'library' is something of an ambibious word. *Normally* (and I believe originally) there where two kinds of libraries: *lending* libraries and non-lending libraries. Both dealth with physical assets (books, scrolls, etc.). These days most libraries are lending libraries, which might also have some items that are not lendable, items that can only be used in the library, usually rare books or things like reference materials (like encylopedias).
More modernly, people have started using the word library in a *different* sense relating to digital assets, as is a 'library of downloadable software or documents'. This is really something different, since the assets in question can be infinitately replicated (copied), and thus the idea of lending makes no sense.
The Web Librarian is really only meant for physical assets that can be loaned out. The download manager is not really meant as a searchable database. It sounds like what is needed is a completely different sort of plugin, something that is something of a hybrid of the two. I don't believe such a plugin exists.