Installed my auxmod in my 06 ST today. Works in all ways, either in ACC, or with the car running, I can move back and forth between modes with no problems. I don't have the CD changer, so I don't know if that would have any effect.
From what I can tell, it's been replaced with a media button in the 2006. Same functionality as far as I can tell though. I'll be installing my auxmod later tonight in my 2006, hopefully at least.