don't know if you figured it out yet but there are two levers on the side of the seat. one on the bottom that allows the bottom to flip up and the second one hides behind the seatbelt on the side of the back rest portion. i never looked at mine close enough to see what size so i believe the others that it is an 8. as for the box, i have seen aftermarket boxes for bigger sizes. when i find it or remember wher i saw it i'll let you know. i doubt the factory amp is large enough to push a larger speaker and get any more out of it than you are getting with your stock setup.