How to wire two additional speakers into my 2000 honda accord?

Currently i have a set of component speakers in the front and set of coaxial behind the backseat powered by a multi channel amp. I also have two subwoofers in the trunk powered by another amp. I also have a pioneer avh x2600bt head unit.
I'm looking to get a little louder and cleaner sound from my speakers and was thinking about adding another set of component speakers onto the rear doors and custom installing them, but i need suggestions on how to power them. Can i use the head unit? Do i need another amp?

You can daisy chain them off of the other speaker. You probably won't get the full power of them if they're better than the others next to them seeing as they will be pushing the same. If you're looking to get nice speakers, tweeters or such, I'd say get another amp and run the wiring. The amp will give you the best power and quality out of the speakers. Just be aware of the amp settings (LPF/HPF). If the amp has a crossover with those options, you probably want to set it to HPF so the highs can come through nicely on those new speakers/tweeters.