Something else I just realized is that the door speakers are a single speaker only, and I'd prefer to keep it that way. The tweeters are already built into the pillars, which is a much better location anyway. Really I think the stock speakers have excellent sound, yet they are crappy quality. I doubt anyone makes a decent after-market single woofer that would replace this one. I'll have to research this a bit more.
While multiple drivers can help on detail and separation, if the driver is good enough multiples are not always needed. For instance, I have two units I use for personal listening: Sennheiser HD58X jubilees headphones for when I’m home, and KZ ZAS Pro IEMs for when I exercise.
The KZs use 8 drivers (7BAs and 1DD) per earbud- 16 total- and can be driven quite easily out of anything. While easier to drive than their more expensive HD600s, the Sennheisers are a relatively powerhungry single driver per ear (it takes twice the volume out of my FIIO M11 Pro’s 3.5 than the KZs do out of the 4.4).
They both sound excellent, and if I really had to pick, I’d say the Sennheisers are better, although the sound is quite different. What I like about the KZs is light weight and relatively cheap $75 price (vs the $190ish HD58X) make them ideal for sweaty exercise- if they get water logged I can buy more.
Not that this is a headphone review, but they both have interchangeable cords and are balanced output capable.
The point is, multiple drivers is not always better.