Something else to consider is that the player has a microphone input. I think using this microphone input would be a much better way of adjusting volume on the player, because you could adjust based on actual road noise instead of speed.

I agree.. i think that the microphone input could be used to provide this function, however i think that rarther than mounting the mic outside the vehicle to monitor noise, it would be better to have the mic inside the car, then have the empeg subtract it's output audio from the mic input signal - the resulting signal would be the noise heard inside the car (more or less). The amplitiude of this signal could then be used to control the volume boost/cut.

Does this sound possible?

RichieC