Might be a stupid question, but I'm wondering if the Shaker pro option from the factory is just an additional amp and subwoofer or is it a different system with multiple upgrades? I'm looking for a car and want the shaker pro as I've had it before and love the sound, but if I find a car that does not have the shaker pro, I'm wondering how hard it would be to get the sound upgraded to be like the shaker pro system. I don't want to change the original Stereo/Nav/Electronic package.