I did it. Took me.. about 1/2-1hour to collect the right tools and unscrew and unbolt everything. Its going to take me even longer to put everything back in. I don't think theres space for an amp. There is no real clearance between the seat and the floor unless you cut into the the bottom of the seat itself which is in my opinion more of a hassle. I can take pictures of the "aftermath" of taking the rear seats out of the hatchback in about 2-3 weeks once I get a camera.
How to remove rear seats? (It's been a long while since I did but heres a rough idea)
Well, I don't remember all the steps but you start by
-unbolting at the bottom of the seats
seat bottom should rise up now, unbolt any bolts you find
-remove the plastic tabs that connect at the rear
-unbolt whatever connects to the seats to the rear
-disconnect the seatbelt tensioners
I don't remember much after that.. basically just keep unscrewing and unbolting stuff that connects to the seats.
Problem is making sure you have the correct sized tools and since Mazda being a "Ford", theres a couple specialty tools you'll need from Sears. I don't remember exactly which ones.. but you'll find out when you start finding bolts you can't unbolt.
I think I just gave the worst advice ever^^^