Hey Mokie , that earthquake amp will br fine for your needs.I'm tring to understand what your'e really tring achieve!
1) i would replace those polk's out for those Hertz, which i think the Hertz can & will sound better then the lower end polk's.
2) deadening your doors & car will hep with acoustics in the car.
3) since you have so many toys to play with i would focus on your front stage.
4) it sounds like you are looking more for a three way combo.
5) if you can go active you'll have more control for what you'll looking.
so some guy built the bandpass for you???
can you take your system back to this guy for help???