If you are not getting your head in the water, the stock Garret Deluxe land headphones are a great deal for the price... I took mine apart and bypassed to volume knobs because they got scratchy from salt water hunting.
I had a set of Garret Blue water headphones and I would definitely NOT recommend them for the AT Pro. They do not have enough bandwidth to reproduce all of the sounds the AT Pro is sending in pro mode. I returned them and went back to the land headphones.
Grey Ghosts, I dunno I haven't used them but I hear they are nice.