Well..Seems I'm heading also for the 50D.
I received yesterday an answer from Telex about why they did not put an auto switch for the Aux. They say it's because pilots volontary asked them to, beeing afraid to be diverted by such music or phone calls...
For sure I won't use this kind of gadget in a TMA or in a traffic pattern, if this one can be used it's in the middle of nowhere. Fortunately there are a lot of such places around the world.