Hey my name is Bo. I'm a bmw guy but just so happened to get my first range Rover! Don't know much about these cars, even more so the ones with the jaguar motors..... Like mine! I have a Black 2006 range Rover sport 4.4 HSE. Non Supercharged. I have the Harmon kardon sound system with the oval shaped subwoofer thing in the dash, and the round sub in the trunk. The trunk sub I'm actually planning on upgrading and I'm having my friend make me a fiber glass box out of the original carpet panel that covers the original sub so I can have an OEM fit and finish looking enclosure but with a 18 inch sub hopefully if he can mKe it work with the required specs needed for the sub in the space we have to work with. If not then a 15 inch sub is the other option. But what would the easiest way be to install an aftermarket sub and amp while maintaining the factory amp for the rest of the speakers and front sub with the factory stereo?