Ricky,
If you were thinking about upgrading the complete system, I would start with taking the complete interior out. The aftermarket specialist will start like that as well (at least if they run wires in a proper way) and therefore I would have them taking out the OEM system as well (otherwise you have to pay two companies for partly the same labor).
The best way is to upgrade the system yourself
! It is always fun to take apart a complete car (or am I just a car-nut?).
greetingz,