Synching iPad with MacBook in iTunes

I use (and have always used) a single AppleID for iTunes. I have added a lot of music directly from the iTunes store to my iPad. I want to make the library stored on my MacBook into my main music library. When I try to synch what is on my MacBook with my iPad - iTunes immediately asks me if I want to delete all the music on my iPad and replace it with the music library on my MacBook. I certainly can't do that since I have twice the music on the iPad as I do on the laptop. I would rather move everything not already on the MacBook from the iPad to the MacBook. Alternatively I could replace the entire music library on the MacBook with what is on the iPad. Can someone offer a recipe???