[Warner306]

So you mean I'm mapping it to the wrong Kodi commands i.e. VolumeUp and VolumeDown are not the right Kodi commands to use for volume up and volume down? Or how exactly do you mean "use as many of the commands read by Kodi as possible"?

You might have to throw out the volume commands and use others. Any command could be set to change the volume. Or, buy an external IR receiver like the ones shown in post #1.

Could you give me an example of other Kodi commands which can change the volume and how to use it? Btw: the volume buttons are working fine in Windows. Volume up button turns up the volume, volume down button turns down the volume, mute button toggles mute/unmute.

VolumeUp
VolumeDown

Those are the commands defined as built-in functions. Choose a key that is read and give it one of those commands.