Bottom line, you are going to spend $800 as an entrance fee just to modify the B&O system with a different amp/subwoofer. Now, you could start with doing the 4 door speakers and two pillar speakers along with sound deadening for those four spaces. When I installed my system, I completed those parts first and there was a notable improvement with just that. Not a ton more bass or even that much louder, but what came out of the speakers was clearer and an overall better sound. Then, save up for the ZEN/Amps/Subwoofer(s)