How do I get the best quality for my system?

Okay so I have a 96 Camaro. Not a big trunk. I have boss speakers in the front doors. Pioneer speakers in back. And Jensen speakers installed in my trunk. I wired those in series with my rear pioneer speakers. I have a 160 watt Jensen linear phase uv9 touch screen head unit. It honestly doesn't put that much power out. I get some distortion with my boss speakers although they are not blown or anything. And all my speakers sounded fine when I had my previous head unit. A 200 watt DUAL head unit. But for some reason my speakers do not sound as good. I wanna replace my boss and Jensen speakers with pioneers so I have pioneer all the way around. Will this help the clarity of the sound? I also wanna get a amp. Used for my Speakers ONLY. I'm not sure of the wattage tho.. And I'm not sure how to wire it in with the head unit. I figured I need an amp for my speakers due to the fact that my head unit doesn't put out much. Will an amp make sound better and clearer? ALSO.. I wanna get a single 12 inch sub in my trunk with a 1000 watt amp or 1200. I previously had a 1000 watt SDX amp and a 12 inch Xplod. I wanna upgrade. To Kenwood or Alpine or another named brand. With this said I would have an amp for my sub and for my speakers. Will I need a capacitor? Probably.. Also would a equalizer help anything? To make sound better? Someone also said something about a line driver? I'm confused.. My head unit has one blue port for my sub. Would I need a Y splitter if the amp, has to RCA cables? If anyone can answer these questions and lead me in the ring direction that would be greatly appreciated.. And would help me loads! Thank you.