You can get a line output converter to do that. $20 at Walmart. You run the speaker wires from the stereo into the box and it gives you RCA outputs. They work pretty well and allows you to keep it stock. Just leave enough wire length to return it to stock when you want to get rid of it.
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