Still doesn't seem right
 

Hey guys,

Well, I went ahead and replaced all 4 speakers with Infiniti reference 6.5's. The fronts seem pretty good, but the rears sound nothing like the fronts and are very distorted above 17 vol. levels. I have adjusted the fader to + 3 to the front and that helped a bit, but still doesnt seem right. I am guessing I may need to replace the head unit(Non Bose)? What do you guys/gals think?

Are you powering those speakers with the stock HU amp or aftermarket one? I'm not sure the stock amp adequately powers these great speakers.

you more or less answered your own question with your first statement!!

speakers are only as good as whats running them!

When you are right, your right. Time for a new head unit.