I replaced the factory stock unit on my P5 with my old head unit that had a "MP3" jack. It's just a 1/8" stereo plug that functions as an AUX input. I use an ARCHOS FM Recorder (20 GB) for long car trips and use a simple male-male 1/8" stereo cord (from Radio Shack) to connect to my head unit. The sound is much better than any FM modulator or tape adaptor I've used in the past. If your want to stick with the factory radio, I would use the tape adapter. I had one for listening to CDs on my old 93 Protege DX. BTW, my head unit is the JVC KD-SH55. Good luck!