After my last entry, I made an additional change that I think accomplishes the what a CEC blocker does. I already owned a Zettaguard HDMI Switch from a previous configuration. I connect my devices to the switch's inputs and the output is sent to my Marantz receiver. If any of the non-selected devices receives a command, the Marantz doesn't know about it because only the selected device is physically connected. And the Zettaguard is in the Harmony's database so selecting the correct input is now a step in the start-up of each activity.