Your amp is a 75x6 amp, correct? If that is the case, I would bi-amp the front components to provide 75 to each driver (woofer and tweeter) and then use the remaining two channel amp to drive the rear two speakers.
Another thought to consider would be to replace the eclipse with some sort of larger midbass (7"-8") to mount in the door and do a kick panel install for the current mid and tweet. In this scenario you could triamp a 3 way component set up front.
I guess what it comes down to is that if you have passengers in your car in the back seat often, you may want to run rear fill speakers. If you don't frequently have passengers, either fill or no fill can be made to work well.
I doubt that cleared anything up but I think Trapps and SVTContour said most of things I would have.
