Most settings not stored in the Library are stored in the Registry here:
HKCU\Software\JRiver\Media Center 15\You can export this registry key to a REG file using RegEdit and then import it on the other login to "copy/paste" the settings manually between logins, or even between machines. USE CAUTION when moving settings between machines, as some things may break. If I'm going to another computer, I usually only export the stuff I
need to copy around, like Toolbar settings and the like, and then manually reset the rest. Also, there is another set of registry keys at
HKLM\Software\JRiver. Don't mess with these. They are machine specific, and don't hold any useful settings (and copying them about will probably break your MC install).
I once wrote a script set that would automatically export these settings on logout and then import them on login. I don't maintain it anymore because I no longer have a reason to do this (I now have either shared logins or user-specific machines on all of my home machines).
However,
I did post them way back when. You might need to modify them a tiny bit to get them to work again (especially if you need to do it on Vista/Win7), but it shouldn't be too difficult if you've ever done any kind of scripting in Windows before.