How to import music in one fell swoop?

Hi all - just upgraded my setup to El Capitan.

I need to get it all set it up and new again but one thing I need is to get all my music back into iTunes. It looks like 90% of my music is there from iCloud, but how can I link my current library (saved to a different HD - iTunes structure intact) and add everything back in one fell swoop? I already changed the library location, but That only works for new additions to iTunes, right?