I prefer Givi stuff to Hepco and Becker and have used both top box and panniers on mine.
I used Fehling racks and frames to do it though. I would imagine the hoop at the front of the oe rack would make it difficult to fit a Givi base plate. Either way you will have to figure a way to mount a "universal" base plate to the rack - not particularly difficult.
One thing I don't like about the Fehling rack is that it fits too close to the rear light. By the time you've put a top box on there any high vehicle behind you would not be able to see your rear light.
I've switched to soft luggage these days. BMWs "Softbags" have a rigid base and sleeve that slips very neatly over the Uly triple tail when laid back and removes the need for all the metalwork. The small one takes a helmet and does 90% of what I needed a top box for.
