Here's the link for the KC OS 6.5 in English:
http://www.access-music.de/downloads...ruskc&file=288
Here it is in German:
http://www.access-music.de/downloads...ruskc&file=289
Are these the versions of the OS you have tried?
I too own a KC and still have the original CD with the factory info on it from the time period it was created in. I actually updated my KC with the English version of OS 6.5 about two years ago (+/-???) and have had ZERO problems, it is a dream to play and work with. Really sorry you are having such trouble. Not having the keyboard of a 61-key Virus is missing a good portion fo the overall experience of playing it. Good luck!
-Alex