well....if you are running the new speakers on the stock system this could be causing the distortion, if you want better sound, possibly better bass from your speakers then get an aftermarket amp, (i have heard the alpine 4 channel, or kicker 4 channels put up great wattage). What i did was get this alpine head unit ( http://www.alpine-usa.com/ ) at a local discount audio shop for around $175....best purchase i made in the stereo "department." It puts out clean wattage just off the unit, no amp at all, i just ran new speaker wire from each new kicker speaker i installed in the back, and since i bought component speakers for the front, just wired the new crossovers, and ran the wires to the head unit... then with adding the sub, i got the perfect sound i was looking for, because of the head unit, you can control the subwoofer, the bass, treble, everything you can possibly imagine, and i have it exactly tuned to how i enjoy it. So, if you have distortion, just run new wires to the head unit and that will iliminate that, but remember if you are running any wires back for your subwoofer, to run the speaker wires as far from that as possible because the closer speaker wire is to a power wire, you will get a distinct buzzins low level distiortion noise in the speaker....(also run your RCAs separate from the power, same deal, distiortion).....sorry if this seems like i rushed, its because i did, i have installed many systems, wired many systems, so i feel confident i could answer many questions you have, so just PM me....