For the door speakers you're honestly not going to get much better sound unless you change out the amp, as it has a low-pass filter built in.
I got much better sound out of the doors by replacing the speakers with Infinity 6032cf 6.5"s (6.75") and replacing the factory amp with a Kicker 11DX125.2.
I'm running the L/R door speakers and a 10" sub bridged to the amp, sounds really good and I spent less than $200. I simply tore everything but the frame out of the door speaker brackets and used some outdoor mounting tape to secure the speaker to it. The solder the connectors to your speaker and you're good.
***Kicker Amp***
[ame="http://www.amazon.com/Infinity-Reference-6032cf-6-5-Inch-High-Performance/dp/B002BZFSYA"]***Speakers - 6.5"***[/ame]
***Sub - 10" - I know, it's DUAL! But I got it on sale for $39.99 and am not sending much power to it***
[ame="http://www.amazon.com/Metra-70-1761-Wiring-Harness-Speaker/dp/B0002BEQJ8/ref=sr_1_1?s=electronics&ie=UTF8&qid=1407527026&sr =1-1&keywords=metra+70-1761"]***Wiring Harness for Amp***[/ame]
I wanted a system that was easy enough to convert back to stock (sans door speakers) and that ran off of the 15A factory circuit.