speaker question
 

i have alpine type x spx-17ref components as front speakers
should i use 2 way or mid range in the back?
whats the difference between mid range driver and 2 way full range?

Difference is what frequencies they should be playing, personally if you must put in rearfill I'd go with just mids, I find highs behind me distracting and annoying.

depends on how you like it.
i like highs in front and behind me.

strictly personal taste. I have to have full range rear speakers, I find the sound without them very bland and lacking in ambiance. The other issues may be, passenger enjoyment of the music...without full range in the rear, it sounds like poo in the back...and the size of your vehicle. I find larger 4 door sedans need full range range rears(for me anyway), whereas I can tolerate front only in 2 seat coupes ( I still prefer to have rears too). Anyway, like I said, it's strictly a personal taste thing. If you have the rears already, install them, you can always turn them off, physically restrict high freqs, or band pass them if you don't like rear fill.

thanks for your answers, now i know what to get