well, the car in question was a 05 celica with the oem headunit no external amp from the factory, and it literally had four speaker wires off the back of the deck. It had two tweeters in front, and midrange (which had factory crossovers for the tweeters) and then rear speakers, so six all together. I first just tapped into the rear speakers to run to the amp, and it sounded like crap, the sub was barely making any noise, and the rear speakers were overdriving badly, I then disconnected the rear speakers all together, and between the front speakers and the sub it sounded great, so i added the left rear speaker to the left front speaker, the right rear speaker to the right front speaker, it sounded great, crystal clear front end and a pounding sub, but had no fader control, so got a wild idea to put the front speakers on the front left and the rear speakers on the front right to have fader controls, I don't usually mess with left and right balance. And the rear speaker wires to the amp were controlled via the true fader control to reduce the bass when it wasn't wanted. It was the one way that made her car sound very clear and none of the speakers were overdriving.
how would you wire it up?