Oh, and you can shut down the PS3 by holding the 'PS' button until the menu appears. Shutdown System is one of the options on there, then press X to select Yes. You should be able to set up an Off macro easily enough, surely?
Is it always that way, even if two game controllers are powered on?
I've seen that "hold the PS button" menu look different (and require different keystrokes) depending on what's happening on the system at the time and where you are in the menu structure (are you playing a game, playing a DVD, etc.)
But yes, it's my intent to create an off macro, I just need to make sure I'm taking everything into account when I do it.