use apple tv remote as a universal remote

The only thing you can do with the Siri remote is to control the volume of a TV or a Home Theatre amplifier. The other buttons and the trackpad talk only to the ATV, using Bluetooth. (Older ATV remotes control only the ATV.)

I would also add that you can use HDMI CEC if supported by your TV and/or Receiver to power these electronics on and off with the Apple TV 4.