Re: Kitchen Island Remodel
I didn't understand if you wanted to remove it or extend it?
If you want to remove it, I would take a utility knife and cut just inside the caulk line on the drywall. I am assuming (dangerous to do without seeing it) that the "box you referred to is a 2x4 frame that stands the drywall off the back of the cabinets? You can tear the drywall off frame and replace it with whatever you would like.
If you want to extend it, then cut the drywall at the caulk line and take off the wood panel on the one end of the island. Add your island extension and match the "box" on the back of the existing island. Then add the drywall and tape and spackle the seam.
Without seeing the exact situation, there are probably some finish details I am leaving out.
Good luck & have fun.