[gsr1379]

So this is probably a simple thing for most people but I am having a hard time finding what I need.
 
What I have
 
Source: imac
Speakers: Event Tr5 Powered monitors
Headphones: denon d2000, senn 555, ie8 etc nothing to demanding
 
What I would like to do is have something that would hook up to my mac and pass audio to the speakers. Then I could flip a switch or plug in headphones and the Speakers would turn off and audio goes to my phones. Best possible solution would allow me to leave headphone plugged in at all times. Just put them on push button or flip switch and audio switches from speaker to phone. 
 
I would like the built in volume controls to reman working at least on the speakers. Sometimes I sit away from the desk and use the remote. If I was using the headphones i knob or something to change volume would be fine. 
 
This would be simple if the speakers had a volume control on them. I could just split the audio out and turn the speakers down. (of course then the headphones would be playing all the time not really ideal) or really simple if I had speakers with a headphone jack.
 
As I do it now is I reach behind the computer unplug speakers plug in headphones. It is kind of a pain and I am sure not to good for the jack or the speakers.
 
So any suggestions would be great. Budget unknown right now I just need to get an idea of what I need. 
 
Thanks