PAC Amppro will not work with basic 6 ch system as there is no Amps.. In either case, w/ or w/o factory Amp., and you intend to add aftermarket speakers & Amps, still better to take your feed directly from factory radio to a DSP and bypass any factory amp. This is one less conversion and noise source than using an PAC. I can tell there are still some people skeptical on using a DSP (i.e. FIX 86) to feed their aftermarket amps.. And if you are using a non turntable AMP(s) you should be. In other words.. you will defiantly need to be able to fine tune your system.. I have a complete aftermarket system while maintaining my factory head unit. The head unit works as the factory intended, however music coming out of my system is mind-blowing. I went my system upgrade with intention to buy an aftermarket Head Unit i.e. Alpine or Kenwood, if i couldn't get decent sounds using the factory head unit. After completing my install, there is no need switching out the factory head unit. It sounds as good or better then the aftermarkets mentioned above. Now,, if you don't go with a tune-able system, then i can't make this claim.