if you dont already have bose then dont retro fit it! its not all that and if you are wanting to fit a better sound system in the car there are plenty of options!
Andy Mac does a really nice stealth sub that sits in the same place as the bose sub so you still get to use your full boot.
also for the door speakers get a decent set of Alpines or JBLs as they will be miles better then the bose setup. you will need to rewire the rear speakers to the headunit as they are currently wired into the crappy amp in the boot.