I just baught a 99 Durango slt. stock it came with the infinity system, but when i baught it, the front speakers were gone and there is now an aftermarket head unit and it came with a 12" mtx sub and amp in the back. i hear nothing but bass. my question is how can i connect the component system up to the factory amp and then have that go to the HU and still have the other amp with the sub hooked up? and is there a way i can test the factory amp to make sure it still works good and everything before connecting all this?