Car Speaker Probelm?? New car reciever or a new amp . I NEED HELP?

In my Toyota Camry 97 i have in the front doors Kicker Component DS6.2 , No speakers in the backdoors, and on the back dash Infinity Kappa 62.9i . I have a regular car reciever a kenwood KDC-4022 . After riden witht them turned up mid/loud they tend to distort and it sounds really ugly. Is it that i need to buy a 100 wat 4 way amp, do i need to buy a stronger indash, Or do i just need to replace the speakers with polk audio? . CAN SOMEBODY PLEASE HELP!!!!