Moving Existing External iTunes Library to new iMac Internal Drive

Recently, I picked up a 2011 27" iMac 3.1GHz to replace my aging 2007 MacBook Pro 2.2. I ran the MBP as my desktop for years. Of course, the 120GB standard internal was not enough for my growing iTunes library. So I ended up moving it to an external drive. After several lost libraries, I finally got the external drive to keep all the metadata and what not. I would like to prevent that heartache altogether this time.

I used the Migration Assistant to move all my setting over to the iMac. Now, it recognizes the external drive as it's iTunes library, and has kept all various other data.

Now to my question:

How can I move everything onto the internal iMac drive, without losing all associated data?