i hear that there is this device that can plug into your antennae input on the HU, and then when you want to listen to whatever the device is hooked up to (mp3 player, cd changer, etc) you can program it to broad cast over a certain "dead" fm station. so for instance when you turn to station 99.9 you will hear the mp3 player. know what im talking about? what is it called? more info please!