the best thing to do is buy an after market head unit and use the rca cables for your subs. Does you amp have a crossover. You can get the Head unit from any store I like the Pioneers for they are cheap and effective. I've had the high dollar head units but still get the best bang for my buck out of the pioneers. You can get a wiring harness at any best buy to ease installation. You might have to buy a faceplate kit. it is worth the money for the stock stereo just does not have the juice to push the rest of the speakers effectively when you have the bass. I've built many a systems. Never have used a stock stereo for that reason. Not to mention you do not have to cut your wires and guess which is pos and which is neg. | 
