With the official launch of stephanroemer.net I also released TotalKeyMix. Now you know, why it all took so long

With this Windows tool you can control the main volume of any RME soundcard (that uses TotalMix) via hotkeys. For example you can assign the multimedia keys (volume up, volume down, mute) or any other key combination you prefer.

Check here for more details:
http://www.stephanroemer.net/downloads/totalkeymix/