Could somebody help me understand car audio amplifiers?

If you like the sounds of your subs right now then i would just recommend going with an amp to your doors. If you're running off a Sony headunit then its only pulling power from the headunit. If you put an amp to the doors instead then you'll be able to draw alot more power to them and it should make them sound a whole lot better. If it were me personally doing it then I would just replace the speakers in the doors with a component set instead of speakers and adding in tweets because it helps a ton just to get the mids and highs separated.