I use mine to work my Roady XM radio and my I-way 500 GPS. Hook up the one you listen to all the time as your primary, and the other as secondary. When you turn #2 on it automatically overrides #1. No switching or input from you, totally automatic.
This is a nice setup, and well thought out. Kennedy has responded well to any concerns I had, also. A class act.
I made a pigtail splitter for the AUX input. I have my satellite radio hard wired into it it as well as the AUX input located in the left pocket for my MP3 player. Of course you should not use both at the same time.