Pop the seat bottom out first (mine came out by pulling hard upwards), then when you look under the seatback, there should be blots (4 or 5, I can't remember) holding it in. Take those out and slide the seatback upwards and out. How are you gonna slide a speaker box into the convertible top bay? There's alot going on back there, unlike the Coupes.
there's only 2 bolts on the bottoms of the back portions. as tallmf said, you just have to pop out the bottom portion first by pushing the two tabs located under the seats at the bottom of the cushion (where the bottom of the knee would be located)
BUT: how are you going to "slide in a speaker box" if you've never had the seat off? there isn't any room really, you'll have to relocate the 'vert top motor that's in there. It's doable... you just have to pop the motor off of it's base using the 4 rubber cones, before you take the base off. Anyways... good luck.
Kind of an old thread but I had a question about the back seat coming out. Once the back part of the seat is out, does the grove for that you slip the convertible boot go with it??? In other words can you put the Vert boot on and have it say if I took my back seat out??