Go into MixEmergency 1.5's preferences, then to the Transition tab of the preferences. In the Auto-fade box half-way down the window there is a "Hot-key" area. Click in here and it'll display "Type shortcut". Then enter the keyboard short-cut that you want to use. Keep in mind that this is a global keyboard shortcut - so it can be triggered while any application has focus, and needs to be something that other applications don't use (e.g. you can't use apple-c for example). I think I have mine set to apple-shift-space, or something like that.
