The first thing i did was upgrade the 6x9's to sony xplod 3-ways with a 200w MTX amp, only because i had them in a previous vehicle. I then added an 8 inch bazooka tube. Most reacently i have added an Alpine model 7893 Head Unit which i absolutely love. I am totally satisfied with the sound of the system. The front stock speakers will eventually be replaced but sound much better with the Alpine V-drive. Just some things to look into.

I would consult crutchfield as to speaker replacement because i have heard many require too much depth for the X. Good luck!