when I import a DXF file, from 3ds max for example, I use the translator "for further editing". In the custom functions I mark the option Polyface mesh>To GDL 3D> Convert Polyface mesh to 3D.
When I import the file, I get it as a GDL object. Is there an option to import the file as ArchiCAD mesh? or better, is there an option to translate the walls as walls, the windows as windows, etc.?