We have been using ogr2ogr to export data from PostGIS into DXF. Using the default behaviour of the export, all data are put into layer '0'. We would put data into a layer name from the PG table name. It is not really clear if the correct solution is manipulating the header.dxf under the GDAL library or if this can be achieved by using some of the command line options from ogr2ogr.
Thanks for any input.