Jeep Grand Cherokee Amp Bypass

I own a 2002 Jeep Grand Cherokee. It currenty has 6x9's in the front doors with tweeters in the dash. In the back doors it has 6.5's. It would be better to put a component 6.5 system in the front with a crossover tying the two together, and just doing 6.5 coaxial in the back. The only problem is that I can't do that with out putting in a new amplifier. I need to bypass the factory amp. I want to keep the stock headunit, but i do not know if i should run all new wire, or bypass the headunit by manually spilcing the wires together. if i dont run speaker wire what is the proper method of bypassing the amp is it to just spice into the existing factory speaker wires and then run them into the new amp? i would apprecaite it if someone would explain how to properly bypass an amp because there is no harness for this car.

yeah i think that is the best way to go. i have the wire colors and i will run the line level converter off of those and plug the rca into the new 4 channel, and then just splice into the exisitng speaker wires that i know the colors for and run those as the amp outputs. is it ok just to splice into those with t-taps? or should i cut the wire and run it into the amp? thanks