Speakers are distorted

Ok... so yesterday I hooked up my new deck.  Pioneer DEH6800.  Its and awesome deck but for some reason my speakers dont like it.  They get all distorted.  I have some little 5 1/4" pioneers in thr front.  And some doodiety hand me downs from my buddy.  The Pioneers do just fine when I put the fader in the front.  But as soon as I equal it out... DISTORTION!!!!  I have no idea why.  And even when I disconnect the rear speakers its the same deal.  So it has to be wiring im guessing.  I know its probably something really simple, but whatever it is I cant think of it.  Any suggestions would be greatly apprectiated.

Sorry.  Its a 1992 Dodge Dakota.

Are you sure they are all wired correctly?'85 Toy

Please describe what you mean by "distortion," as there are several things that could be happening.  How loud are you playing the system?  What's the impedance of the speakers?  Is it just one speaker per side? Support the12volt.com

what happens when you adjust the balance from center to left or right?

In reply to them being wired correctly me and my buddy have gone throught everything to try and pinpoint whats going on, and so far nothing has changed.

Here are the speakers I have in the front:  http://www.pioneerelectronics.com/pna/v3/pg/product/details/0,,2076_310069908_291215780_tab=B,00.html?compName=PNA_V3_ProductDetailsComponent

I have completely disconnected the rears and nothing has changed.  The distortion sounds like the speaker is blown.  But like a said, I only get that sound when I fully mix the front and rear.  Switching from side to side does nothing.  Doesnt matter if its a full mix or if I have it on the front.  When its mixed and fully to the right it sounds like crap.  But if its only in the front then it sounds clear as a bell.  The player volume goes to 60 at about 40 it does the cracking.  But only when mixed.   Fully front is totally clear.  I only have a 4 speaker set up right now.  1 in each door panel (2).  And in the rear corner panels (2).  I havent hooked up a sub or anything yet.

Maybe it could be that those crappy rears can't handle the power...If it sounds clear up front and *bad* in the back than try replacing the rears with something better.The pioneers can prolly handle the deck's power better than the rears...also that link doesn't work.