some amp advice help me out!!

Hello there. I'm a newbie at the sound systems stuff, but i have installed a new kenwood headunit and all new infinity kappa speakers everywhere. I'm not quite ready to go to subs so i was thinking of buying a 4 channel amp and powering the door and rear speakers with it. But i want to know what kind of difference it will make....will there be lots better bass, highs? the speakers distort right now but they are only getting 22 watts rms and they only distort when the volume is turned almost all the way up. So i believe the speakers are underpowered. If i should get an amp, what brand and what output? the rear speakers handle 100 rms and 300 max apiece. and the doors handle 75 rms and 225 max apiece. The speakers are also 4 ohm impedance so that means i need to run the amp at 4 ohms too right? anyway what is a cheap but very good brand, (works great but doesnt HAVE to look good) and what power output should i probably get? thanks alot for any help in advance because i NEED it!!

i have 6.5's in the door and they actually put out better bass than the 5x8's in the back. But the back speakers have terrible damping so i need to get a damping kit for them and the doors. i'm planning on spending really whatever it takes for a nice, clean, and POWERFUL sound from them.

well i might do that, but i really would rather just keep the current speakers because they have the adjustable tweeter and its pointed right at my ears and it sounds awesome having highs comin from the back too. i really think they are incredibly underpowered since they both hand at least 75 rms but only get 22 dont ya think so? a new amp should improve it substantially not to mention some sound dampening.