You can't just plug in your amp to the factory radio, you need a HI-level converter to take your speaker level wires and convert them to an RCA output. You don't need to pull out the radio for that, just locate the speaker wires and tap into those, then locate an Accessory wire to make the amp turn on and off. Then run a wire to the battery for power.
2006 SE 6 Speed, Solar Yellow. Zone 2" Hydro BB, Sway Links, and Steering Stabilizer. 31x10.5-15 Bridgestone Dueler AT Revo. Alpine CDA9813, Polk MM6, Polk C400.4