Apple TV control external HiFi - difference between direct control or Airplay I have my TV connected to my Apple TV 4K over HDMI. I've connected my HiFi over a toslink (optical)connection.

Now there is a difference in controlling the volume if I use an Airplay device or the Apple TV itself. 


If I play music from my iPhone via Airplay to the Apple TV, I can control the volume via my phone. That is, the volume of my TV-speakers and the HiFi is changed.
If I play music directly on my Apple TV and control the volume over the remote, just the volume of my TV is changed. That is, the TV-speakers are controlled, but the HiFi remains at the set volume. So I cannot change the volume of both speakers. (Additionally I see also the volume bar of the TV)


Can I change the behavior of the remote/Apple TV/Audio, so that it behaves the same as the first case?
In order to control the volume of your HiFi, you will need to use HDMI-CEC between your AppleTv and your Receiver/HiFi. Data (audio) transmitted over optical is sent at a fixed volume, and relies on the receiver of the signal to control the volume. 

If your receiver does not have HDMI with ARC, you may be able to get around this in the following way:


Connect AppleTv to TV via HDMI
Connect TV Audio Out to your Receiver.
Configure HDMI-CEC to control the volume on your TV from the AppleTV remote.
Configure TV Audio Out to be "variable", not "fixed" or "line level". This step will vary wildly depending on your TV.


There will be tradeoffs depending on your TV &amp; Receiver's input/output options.