and a 3 way setup (esp run active) can out preform a 2 way setup.. but with the amount of work.. tuning..ect... it takes... its usually easier to just go 2 way... also a good 2 way setup will sound netter than a bad 3 way install...
From what I read in here is that rear speakers are a waste of mone along with the 4 channel amp, I have a crew cab truck, and the speakers sit low in the door panel, so skip the 4 channel and do a set in the front with a two channel amp?