Update: Well, I can't find anything about this in the user manual, the Master Volume Knob should work, but it is not working here. So, I will be returning it to my dealer, this must be a HW-Issue with my REV2.
Update 2 : OK, I got to fix the issue, I had set the Pot Mode to 'Relative' which disabled the functionality of the Master Volume Knob (This might be a bug that needs to be fixed).
It worked as it should when I changed the Pot Mode to 'Jump' or 'Pass Thru'. So, I'm glad this was not a HW-Issue, but just a setting that affected the functionality of the Master Volume knob.
I'm wondering if this is a software bug that should be checked by DSI Technicians ? Since a 'Relative' knob behavior should not disable the Master Volume Knob from functioning.
Hope this info. is useful,
Muziksculp