2004 S4 avant-MP3 add-on
 

I just bought a beautiful black 2004 S4 Avant which has a Symphony stereo in it. Has anyone added an MP3 modification that will work?

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Depends on what options your car has. I just went through this same process. If you car has steering wheel controls a Ipod adapter will work pretty well. However if you dont have steering wheel controls for your stereo it will not display song names and artist. I just ended up going after market.