Searching on internet showed the name oris as assocaited with bosal
http://www.oris-gmbh.de/Oris-Matic/E...rzeuge_EN.html the link does not show bmw x5 compatability. Bosal do make towbars although the bosal ones I have seen compatabble for E53 are swan neck and not detachable like the oris.
I know you're not in the UK but if I fitted one I would probably keep things simple and go for the westfalia detachable.