I'm sure you have read the info at
http://hauptwerk.co.uk/UserDoc-160-OperatingOrgans.html .
I'm not sure how your MIDI keyboard can send the appropriate signals to activate registration frames. The computer keyboard works fine. With registration frames as they exist in Hauptwerk, there are adequate numbers of frames to allow for multiple instances of the same registration. Serial access works fine and random access doesn't seem necessary.
I hope this helps.
Cole