the best method I get for now, is to export the 3D model from Archicad as Wavefront object (.obj) and to to import it in 3dsmax. The model is imported as editable poly. You have to work a little to attach the poly's because they are split in two parts the smooth and the flat part but it worth because you get a much smoother result in case of curved objects and terrain mesh compared to the .3ds export, and you can further improve them in max.
If you have earlier version of max you can download an .obj importing plugin from http://www.maxplugins.de
If you have to change a part of the model you can delete that part in the max scene and to import again the modified one from AC, remap and render.
Hi guys. I know this is somewhat old, but recently stumbled upon it after a search.
The feature you want to "update" your 3dsmax model is "there". The .obj workflow will overwrite a lot of stuff on re-import.
The workflow I use, and is quite effective and something I've been using for some time now is: archicad->.3ds :export as 3ds, set up scale, export by materials. .3ds->autoCAD :IMPORT .3ds into autoCAD, ADD all objects exported in the import dialog box, tell autoCAD to create layers by object (this will create objects by material in autoCAD) autoCAD->.dwg :save your imported .3ds geometry as a 3dsmax compatible .dwg (just make sure your 3dsmax version reads the .dwg output) .dwg->3DSmax :use the file link utility to import the autoCAD .dwg file. Adjust the settings and create a standard import options file.
If you later change something in AC, add objects, remove them, etc, just keep an eye on your materials. Export the .3ds again, in the autoCAD .dwg erase everything and reimport with the same options, save again to the same .dwg and in 3DSmax, just update the file link.
This workflow WILL KEEP ALL YOUR MATERIALS ASSIGMENTS (if specified in the reload options) AND ALL YOUR UVMAPS AND MODIFIERS. It will just update the geometry.
In the end, it would be like exporting a .3ds from archicad, but using autocad as intermediary to be able to update the geometry.