Hello se77e,
All 3d software has a spatial limit which is around 80km for Archicad. It is then necessary to draw close to the absolute origin of the working file.
To have a DWG with the project-specific reference system, all you have to do is compile your DWG from archicad in a worksheet in which you have previously discarded the reference DWG (far from the origin). Once your DWG is repositioned, just re-publish your DWG from the worksheet.