@zing Many thanks for the detailed response.
Yes I am not using a TV, just an old laptop sort of repurposed as an arcade cabnet I guess thats easy to pack away or move into another room. Screen speakers etc all in one.
I had a look through the Hotkey+B menu and can see gain control but no master volume control.
I guess what I am looking for is a way to have the underlying os map a command to the laptop keyboard?
So that I have the same volume control of the laptop if it were running a normal desktop OS.
What is recalbox built on?