Hello Tim,
iTunes has (at least) two ways of storing metadata. The conventional way, which is in tags written inside the files is one way. The other way is the vast iTunes XML file. I think you might have to do an export or something in iTunes to get that xml file. I honestly can't remember as I haven't messed with it in so long.
If your tags (Artist, Album, Song name, etc) are in the files, then you can just import the files directly and MC will read them and populate MC's internal database.
I suspect that you probably have other stuff you want to retain. Maybe song ratings? Those are normally stored in tags inside the files too, but might require a bit of messing around as I'm not sure what the tag name is and if MC reads the iTunes rating tag or not.
You might also have playlists you want to preserve. If you have a few (let's say 20) then you can export them one by one and import them into MC one by one. If you have a BUNCH, then you'll want to try the iTunes XML route.
My knowledge of using the itunes XML file with MC is nearly zero. According to this post, the process is pretty simple:
https://yabb.jriver.com/interact/index.php?topic=121730.0This wiki page might also have some useful information. I see there is information near the bottom about iTunes playlists:
https://wiki.jriver.com/index.php/ITunesI hope that gets you started in the right direction.
Brian.