For serious In Car Entertainment, what you need most of all is a set of HUGE subs!!!
Preferably bigger than the car itself!!!
I will try adn find some proper pics of this car so you can see what atrue setup should have. It even has ports for connected turntables to!!! And somewhere of the net there is a video of it where the vibrations from the subs are enough to flip a doughnut off the roof of the car!!!
EDIT> it is capable of over 135 dB in normal usage!!