How big is the male? If he's fairly small I'd recommend getting one about the same size. That will at least give him a fighting chance when you add one. You could get one that is slightly bigger but not too much bigger.

Maroons can be pretty vicious. I would keep something around to divide them if needed. It may actually be a good idea to get some sort of hang on basket or hamster ball to keep them separated until they get to know each other a bit.