Well you've got most of it covererd there. The big square pieces are the coils to make it a deep system that will go very deep on larger targets. The smaller coils are for more general detecting.
luvsdux
Nice set you got there, I hope your a bit in shape though, that GTI 2500 will give you one heck of a workout, especially with the larger coil. Good detector though. The larger square detectors are the treasure hound option for it. Simply do a youtube search of GTI 2500 and Treasure hound and you can see them in action.