While I don't know the exact depth. I did replace my door speakers last weekend and unless you have a gigantic speaker, any 6x8 should fit. I doubt like a 9-10" woofer would fit depthwise though, unless it was slim. (I realize the bose is 9" fronts i think)
In fact, from memory, I dont think the windows go down far enough into the door to hit the magnet even if the magnet went all the way to the door frame. I'm going to rerun some wire this weekend probably. I'll measure then maybe.