I have a pioneer avh3400 I want to keep the speakers and sub running through my factory harness. However I also want to install 2 powered sub woofers and 2 6X9's in addition to what I have. Do i just plug the amps into the head unit's preouts? There are 3 of them, and does it matter which ones I use? Will using the preouts have any effect on the factory set up?