I would look into a NC50 Nevo Connect and a Nevo Video Sensor.  

The Nevo Connect will give you more reliable control and allow you to connect additional sensors (such as the video sensor)   

the video sensor plugs inline on the video feed from the cable box out to the tv and lets the Nevoconnect know when the equipment is on or off.  this way you only send the power command when you need to.

If that is not an option, you could just throw a power button on the Cable TV page for the cable box.  That is what I have done when a Nevo Connect was not in the budget.