Unfortunately I don't really know much about the Onkyo receiver. I'm guessing that you've checked Remote Central for some files like this. Do the input commands serve as discrete "on" commands? If so, you can always rig up a discrete off command by combining an input command (thus guaranteeing that the unit is on) with the power on/off command.

I used the MX-500's M1 and M2 macros for power on and power off macros. It worked well and was easy for my wife to remember. You can also create some extra buttons on each device as a safety measure - such as "TV ON" on the Dish device in case the TV gets turned off (or doesn't get turned on) somewhere along the way...