Hi bartosh, there's also an OBJ to 3DM wireframe converter here:
http://moi3d.com/resources#Obj23dmWireframe_converter

That will load an OBJ file and save out a 3DM file that has line segments generated for the polygon edges.

DXF export from Modo probably makes what's called a "polyface mesh" entity in the DXF file, which is a polygon mesh made up of triangles and quads. MoI's DXF importer does not read those types of entities out of a DXF file, it only loads wire type entities like lines, circles, arcs, polylines and splines.

- Michael