To keep your Yamaha Receiver from changing the audio input when changing to Fire Stick TV on your LG TV or other TV manufacturers, you'll want to program a "Scene" using the remote for your Yamaha Receiver. Here's how to do this:
1) First, turn on your LG TV, then with the LG TV remote change to Fire Stick TV input (ex. HDMI 1 is where Fire Stick TV is input on the LG TV).
2) Now use your Yamaha remote, and click on the "Input" button left or right arrows to change from "AV1" to "Audio1"
3) Then on the Yamaha remote press the "Scene" button to change to the Scene number (1 thru 8) that you want to program. For this example, I'll use the "SCENE1 Movie Viewing".
4) Now hold down the Scene number button "1" on the remote (for about 5 seconds) so that Fire Stick TV pairs up with "AUDIO1"... the front of the receiver will read SET COMPLETE.
5) That's it... hopefully that works for you. Now when you switch back and forth from Fire Stick TV the audio output should remain on "AUDIO1", and not switch to AV1.
Here's what Yamaha says:
***Make sure the Yamaha receiver is powered on and that you have clear sight to the front panel display of the receiver.***
To reprogram the scene buttons - use the Yamaha remote to first select the input that you desire - for example HDMI 2 - and then on the Yamaha remote press and hold the scene button that you want to pair up with HDMI 2 until the front of the receiver reads SET COMPLETE. The scene button is now reprogrammed to the input that you selected.