Seems like a hefty price to save yourself from unplugging and plugging in a cable.
You could just get a couple of those stereo mini jack extenders, plug them into your xbox and PowerMac and have the female ends on your desk somewhere, or somewhere easily accessible, so that it's quick and easy to unplug the jack from one and plug it into the other. It takes about a second and a half and saves you eighty-five dollars. Minus a few bucks for the extenders.