07-18-2013, 11:01 PM
Okay. Ultimately what you should do is fuse these collections into one in the iTunes library. Here's what you should do IMO:
1. COPY not move COPY the existing iTunes Library (the entire iTunes folder it is in) to the new external drive you want to use.
2. Open iTunes holding down the option key, it will ask if you want to create or open a new iTunes Library. Don't create a new one, just point it to the one on the new external drive. From now on, it will use that library as the default.
3. Okay, so that's all your Mac's iTunes music sorted. Now Phase Two: copy the "old external" music files into one folder somewhere (on the new external if you want). It doesn't matter if you keep your folder hierarchy or not, we're going to be adding that music to the "new" iTunes library so iTunes will re-organize it as you had it anyway.
4. Drop all those music files into iTunes' open window: this will copy that music into the iTunes library and organize it automatically (depending on your tagging).
Now your iTunes Library should be unified. You can get rid of the old external drive's files and folders wherever you copied them to. You're done.