Hi, yall. I ride a 07 electra classic, I have a aftermarket sony head unit, with 2- 5.25 front speakers. I want to add 2 rear 6x9s and install them in my hard bags. EVERYWHERE that i read i hear about guys adding an amp when installing rear speakers, can someone tell why this is? I mean, I have 4 speaker connections coming out of my head unit, cant i just plug the 2 6x9s and go enjoy my tunes? NEED HELP clarifying.. thanks..