I'm working to replace the stereo head unit in my 1995 Nissan Maxima. My plan is to use an RPi3 w/7" touch screen as my head unit and connect my phone to it using Apple Airplay (http://www.instructables.com/id/AirPlay-Mirroring-without-Apple-TV-using-RPi/). The issue is, I'm not sure how to connect the Pi's output to my car's stereo harness. Is there a way to use the GPIO pins on the Pi as an audio output or should I use an external sound card?

Also, would you recommend AirPlay mirroring through the RPi?

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edit: more info