It works in BootCamp Windows
I use a mini DisplayPort to HDMI cable with sound capabilities (bought at the Apple Store). I go back and forth between Windows and Mac OSX, the dammed job forces me to do Windows... Yet, actually, it's only in Windows that I can use the keyboard's volume keys to control the external monitor's volume. I don't understand, I did not have to configure anything it just worked from start in Windows yet I can't find the option in Mac.