Slight distortion in Components

I installed two Polk Audio 6500s in my front and they are right now running off a Premier 6700head unit without an external amp.  These speakers are rated at 10watts to 100 watts and the head unit is 50x4 so probably like 20 rms x4.  Anyways, I've noticed some slight distortion every now and then in what sounds like the guitars or maybe musical peaks.  My question is, is there any way this distortion is caused by underpowering the speakers?  At the most I'm running the headunit at 33 (60% the max volume) which would seem low enough not to clip the signal to the speakers.  I've also turned on the LOUD setting to a moderate level to boost the bass up a bit though.  Maybe the speakers aren't totally broken in but I've heard people say only subs need to be broken in.  I plan on putting a 50x2 rms amp soon for the front comps but don't have the money yet and just got the speakers and HU in after christmas.  Anyone know what could cause this?

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Also, I'm not real sure on how HU work but I've faded the speakers to mainly the front (80%).  Does fading allow more watts to go towards powering the front comps?  I've read that 50x4 means that at any given time the whole head unit can produce 50 watts peak but if I cut off the rear fill speakers will that allow the HU to distrubute more power to less speakers (front) making the rms go up for those speakers?  I hope that makes sense. 

Chilly out, isn't it?  ;)

When you fade toward the front it is the rears that are affected, not the fronts.  The rears are attenuated rather than the fronts being amplified.  The amp can't make more power but you can take it away.

And the poor sound quality you are experiencing is most likely due to the fact that you're using the head unit's amplifier to power the speakers.  If you could cut the low frequencies at about 200 Hz or above the sound would clean up a lot.  But the bottom line is that if you have any kind of a critical ear at all (and it seems that you do), you need to properly amplify the system.

Oh, and for the last question:  no.

yeah, I forgot what boards use the break codes.  Obviously not this one.   So basically cut the bass down and it will clear up........get a amp and crank it all clean!  Thanks