10:4.
I used to be on Ford Truck Enthusiast and there was extensive talk between several members (several were in high end car stereo biz) about upgrading stereos, adding amps, etc to factory systems with DSPs.
I thought the same may exist here...
I realize there could be real implications changing out speakers. Google wasn't much help other than to overview the issue and warn that a higher impedence speaker could overheat the factory system...