I don`t know how well-known Spotify is in the US and outside Scandinavia or Europe. The Spotify app are mainly the reason why I want to buy a Android unit.
So maybe it could be interesting for you to try it.
With a Spotify Premium you could have offline playlists, it would be perfect to park the car in the driveway, connect to wifi, and mark all the playlist you want to play offline, and you could use your pc to create playlist, import playlist from your friends and simply play everything in your car, without thinking about downloading music, use cd`s or memory cards and so on
Check out their website, it would be great if anyone could try it and see how it works!
Unfortunately, it is not free. But it is absolutely worth paying for. Especially since you could have offline playlist on three diffrent units, like your Dynavin in the car, your phone and laptop