Hi,
Got RPI3+HIFIBerry
no knowledge in scripting 
I'm trying to look for solution that each time that video will start he will ask me in which output device i want to use (instead of going to Settings->System->Audio->Audio Output device each time)?
OR
Option to play the audio in all output devices at once
TNX.
It is technically possible, but would require you (not us, you) to rewrite the skin to add the pick/choose function.
There is an addon that switches audio device. You can map it to a remote button to toggle the device until the one you want appears. I use to have script for this, but the addon is much better implemented since is cross platform, I had the audio devices hard coded in my script.
If I am not mistaken this is the addon
GitHub - Helly1206/script.audioswitch: Kodi audioswitch addon to switch between 2 audio outputs
