There are a few things that Tesla didn't reinvent in designing the Model S and one of them is audio, which is fine because that has been engineered pretty well. But, for version 2 of the Model S they could make a bang if they apply this technology: <a href='http://www.ted.me/directional-sound/'>Directional Sound</a>
I could see each seat being it's own audio zone where occupants have control over their own audio experience. To communicate better, microphones which are out of the path of the directional audio would pick up ambient voices and play them as part of the audio to listening passengers. Phone calls would act in a similar way allowing for some privacy.
Kids that want to listen to their new-age music, a.k.a. noise, wouldn't ruin the driving experience.