Here's what you need to know:
When we say "Library" in MC, we mean the *database*. So, in Library manager, when you add a library, what it's really asking you for is the directory where you want the database files to be. These files are very small. Just a few megabytes. I have a folder on my main drive called something like JRiver\libraries\ . Inside there I make additional folders for each library I want to house. So maybe you could make a folder called "lowres_lib" or "lowres_db" or something. Then do your Add Library and point it to that new EMPTY directory.
Once you've created your new library, it will be empty of data files. This is where you either:
A. Set up auto import to monitor the folder with your low res media files. OR
B. Do a one time import of that same folder of your media files.
Then you're all set.
Generally speaking you really don't need libraries for separating different resolutions of media. MC's powerful view system can let you easily access the files you want in the way that you want. Just realize that when you make new libraries, you are setting up some hard limitations:
Combining libraries is very difficult , especially if you have playlists you want to preserve.
Switching libraries is relatively slow.
Of course you can only see one library at a time.
Good luck with your project.
Brian.