It seems the problem is solved with the release of Cubase 7.
Cubase 7 seems to load the LM4 to the instrument rack. It seems to be possible to run the whole bunch of Steinberg products on one computer again. So is the case with Model-E and other legacy instruments. It is not necessary to have a second computer with windows XP any more to run the LM4 Mk II.
If anyone had the same problem with Cubase 6.xx and Windows 7 with the LM4 MKII, updating to Cubase 7 solves the case.
Good luck and thx a ton, Steinberg. This is good product policy finally.
Regards
Wolfy