I've got a set of JBL GTO 626's in the rear doors for experimentation, I've ran amped and on head unit power. Unamped, they will sound okay, but not get very loud. I then ran 60 and 90 rms and they did get relatively loud.

Amp power is cheap, invest in one.

 

^Definetly agree I dont even run speakers off of my deck and have shut off the internal amplifier for stronger voltage and signal output. For the price of some 2/4 channel amps it is definetly worth the investment. You dont want 500 dollar speakers to sound like shitty stock ones.