How should I stop media players from constantly auto-starting? I have a lot of problems whenever I install media players. Some times one will trigger another player, othertimes both players will be triggered if I plug in the aux output cable into my car. Othertimes pandora will keep starting and stopping very rapidly (a bug) when I plug in the aux cable.

Here is what I want:
No auto starting ever, at all. Is this achievable with a simple imperative setting?
You can use the Autostarts app (requires root) to modify which apps can listen in to particular events.  In your case, you'd remove the media player apps from listening to the event(s) triggered by plugging in the audio cable.