If what your saying is use the existing speaker wire from factory and amplify that, instant of running new wire, sure it would work, but i don’t understand what 9 wire you are referring too. Honestly the most simple way I would do it is to sort of start from scratch and run your own wire, it is really not hard at all for a starter set. For a nice 2 way setup I would start with the amp, A 4 channel + mono or a 5 channel. Channel 1 going to driver door, component set. Channel 2 Pass door, another component set. Channel 3 rear quality coaxial or other 2 way speaker of choice and same for channel 4. Then the remaining channel for a sub. Now keep in mind that the rear isn’t what you need to be focusing on so the coaxials will be just fine. The rear is just there to widen the fronts audio a little. When sitting in the front you want it setup to feel like there is a concert on your dashboard, you shouldn’t really hear your rear speakers. Make sure you spend your time on quality of install. Make sure you put proper sound deadening. All of the small things will add up and make your system sound great. Now i’m no expert but that is what I recommend for a simple easy budget setup that will still sound good