I use an Ipod for break music through my PA. I don't use the headphone output, I use an adaptor that has an Ipod multipin connector on it ( like the USB adaptor that came with your Ipod) only it has left and right RCA out connectors, and a 12v input for charging. This adapt. was designed for use in car audio application but works well for adding an Ipod to any system with audio inputs. I don't know if you can listen thru the HP out while the multi pin connector is plugged in or not. I guess you would have to try it. However I'm sure you could monitor the Ipod from the HP out on a mixer board.
Regards,
Jenks