Can we get control of the Master Volume using keyboard commands or via the GPIO?

My player audio goes into a "room mix" and when I need to lower the players volume, I have to turn off the player, as adjusting the room mix volume affects EVERYTHING in the room.

This would be easily resolved by adding keyboard shortcuts like Ctrl + Up/Down for granular volume control, and Ctrl + Home/End for Mute/Unmute.
Allowing a custom widget/app to control this via GPIO would be perfect for my needs, as I have prescense detection hardware that could lower the volume when no people are detected in front of the screen. I can imagine a "mute/unmute button" app being very handy.