I've found that educating users doesn't always work. The solution is to make the software act like the user expects it to!
It already does. Of course the more users you have, the more different expectations you will run across. Having a separate share for every drive makes less sense to me than having a single one. LMCE knows about sub directories and the whole point is to isolate or hide the directory structure based hierarchy. The user doesn't need to know or care where media is stored, and it will make intelligent decisions where to put stuff if you don't try to do manual things. I admit I'm guilty of ripping my [legally bought] DVDs on my desktop and copying them over, but I know it's not the lmce way to do things and I accept the added hassle that comes with it.
The # of users is going to be the # of guests that come over, so quite a few.
Is LMCE that complex that people don't know how it works? Can I search the code somehow to see what might be hard-coded to use public there?
Why do you think nobody knows how it works? You are telling us how you want it to work (counter to it's design), and a couple of us are telling you how it really works and giving you ideas on how to make that work for you. I suspect a number of other people just read the thread and ignore it. Not because they don't know, but because you are asking for functionality counter to the intentional design and they don't want to get into a back and forth discussion on why it is the way it is.
Instead of trying to change the way LMCE works, to trying to mess with links, shares, mounts and such that will get you in trouble, lets go back to what you are trying to accomplish.
You plan to have guests over that will dump videos, music, whatever onto your server. Ignoring the obvious questionable legality of it all, are these people going to be using one of your computers or will they be using their own laptop?
Your computer/desktop/whatever: Just make a desktop shortcut to the correct sub directory and have them use that. This is easier than anything else.
Their laptop option 1: Tell them to drop the files in your sub directory. You are already telling them the server, public, videos/audio/pictures/whatever, already. One more directory is NOT going to be that much more to learn.
Their laptop option 2: Either create a shortcut for them, or walk them through making the shortcut the first time. After that they just use the shortcut and are done.
Manual approach: Let them drop stuff wherever and simply move the files from your small hd to your large one. LMCE deals with this automatically, and the only oddity I know of is if you go into media sync and click the button to show missing files you will see all the files that LMCE knows USED to be on your smaller drive. No biggie.
Don't like those suggestions 1: I'm not sure of your setup, but you may be able to configure your 3TB array and your small drive to appear as a single 3+TB drive to the OS instead of multiple drives.
Don't like those suggestions 2: Put your 3TB on a NAS. Let LMCE pick it up and use it in it's own way, and have your guests drop stuff off on the NAS directly, not going through your LMCE shares at all.
Don't like those suggestions 3: Mess with links, mounts, manual shares, etc. There is probably a way to do it without breaking stuff. Just don't ask us how to fix it.