To clarify I’ve got Apple TV 4th gen! (No optical out) This is probably why the things I wrote don’t make sense!
But anyhow;
Ok, so. Let’s gonover my network:
I have broadband via fibre. The house got Ethernet sockets in the walls. All the sockets are then connected to a switch WITHOUT any wifi functionality.
The airport express is connected to the switch and takes care of the WiFi inthe house. It’s also connected via Ethernet to the Apple TV.
I can use airplay from phones to stream to either my Apple TV or airport via wifi.
When I watch something on the Apple TV (not via phone airplay, but Netflix app on the Apple TV) it streams via Ethernet via the airport express (which is connected to internet via my switch that came with the house.
In the menu of the Apple TV you can then choose Airpirt Express as the audio output - This is a fact! And using Airplay speakers (wireless) with the Apple TV is a functionality that do exist.
If the Apple TV uses airplay technology or not to accomplish this - I don’t know.
And the only output for audio on the Apple TV is HDMI (as stated here: https://www.apple.com/apple-tv/specs/ ) there’s is no optical or analog output.