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I am in agreement with bluespark. Having a quality universal remote is IMO vital to a smooth running AV system. There are just so many variables that assuming that the ATV on/off commands will always do what is wanted/expected is likely to lead to frustration.

I have used Harmony remotes for years. The nice thing about the Harmony remotes is that they have a Help button that will send commands to your system, and ask you in the LCD display "Did that fix the problem?". If you answer yes, the help routine stops. If you answer no it will try another command. Ultimately, your system gets back in sync.

For me, I use the Harmony almost exclusively for system control. The only reason I grab the Siri remote is that scrubbing and navigation is faster with the touchpad than using the arrow buttons on a remote.
 
Just did what somebody earlier suggested with my Samsung TV went into HDMI-CEC settings and told it to say no tho any CEC requests.

Now works perfect press select on remote and TV changes to correct input for Apple TV. When finished put Apple TV to sleep and it changes back to the TV input leaving TV on.
 
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