Dear Mark,

Thank you very much, things worked out fine exactly the way you described 
them. Probably a typical beginners mistake to use mm rather than voxel 
coordinates. The  addition of the     -thr 1e-8 before the -bin made the 
second command work just fine aswell. The compution time was not 
suspiciously long (somewhere around 30 s I would guess).

Thank you very much for your help,

all the best,