I have a Kenwood DNX6990HD head unit, I am planning to add two Polk DB6501's in the front doors, a DB351 for the center channel and two DB651's in the rear doors for the rear fill. Now my question is do I need an amp? I bought the head unit figuring it would help power a set of aftermarket speakers, not sure if I really 'need' more power. If so how many channels/power would I need? Not sure if I would run some type of bridged setup or if I would need a channel for each group of speakers.