Unfortunately, this seems to mean that the Mountainuni system is not truly compatible with the Schlumpf hub, at least not without significant risk of destroying the bearings. If I’m missing something, please let me know, because I’d really like a disc brake on my guni. But I’m not willing to directly contradict Florian’s advice to not use spacers with the geared hub.
P.S.: I’ve got a new-in-box unused set of Sinz ISIS 155 cranks that I’ll sell cheap if anybody wants them.