speaker distortion at higher volumes

I have an 03 Denali with:

Kenwood DDX8017

Powerbass Extreme 6.5 component set in the fronts

Pioneer 4 way 6.5 in rear doors

Kicker SSMB8 as my sub run by a Hifonics amp

My problem is at around 25 on the volume all of the speakers start to exhibit bass distortion.  I am inclined to think that the signal is dirty around this area, but I would much appreciate some input from y'all.

Thanks,

Todd

Quite simply you are exceeding the capability of those speakers, with deck power. Add an amp, and use the high pass filter in conjunction with your subs low pass filter.

So the P-EQ that the Kenwood has won't allow me to dial the bass out of the speakers enough?

Are the amps just more tunable?

thanks,

todd