Without querying the SMS box for it's power state and issuing the appropriate discrete power command, you can never have a completely working power toggle button for it. Even if variable states are implemented (which may work most of the time), the states can become incorrect as devices can still be turned on or off manually, by power outages, etc.

ProntoScript will be needed in order to accomplish what you're trying to do. For the sake of simplicity, I'd go with the previous posters' suggestions and use 'power on' and 'power off' macros that use your discrete codes.