Check it out here. Some minor upgrades required, but it works!!

Installation Guide (http://www.angelfire.com/trek/grochef/index.html)

How do you control your MP3 Player if it's back there with the modulator?

I ran an audio plug to the front of the car. I can control the MP3 player from my front seat. So far that is as good as it gets for owners of V50s or S40s. The iPod cannot be controlled from the head unit either.