I am sorry I will have to disappoint you! The kind of conversion you (and me) imagine is impossible! And this is ArchiCAD's fault , not AutoCAD's!
ArchiCAD cannot separate different materials when it imports objects from any other file format - neither dwg, nor 3ds! For example the sink tith the tap consists of two objects/materials - the tap and the sink. I have separated them both in the 3ds and dwg files, but when they are imported in AC, they become one object! The 3D Script consists of description of about 1200 planes and edges and it is almost impossible to separate them!
There is one more glitch I found - when dwg is imported, it preserves the original geometry ot objects, while if 3ds is imported, AC smooths everything, even the most sharp edges!
I am deeply disappointed from AC!