Quite some work, but at least acceptable: grouping things together per texture in MED -> exporting to fbx 2005 -> converting to obj -> adding the texture names into the objs .mtl file -> importing into blender with the groups -> assigning the textures in the correct order -> joining the groups together -> DONE.

Quite some work, but with 3 to 10 textures for 7 models as it is the case for me, this at least works.