I finally managed to convert the dsf file with XPtools after creating an overlay from it thanks to ortho4XP.
The resulting txt file lists which elements are used there. This narrows the choice :
https://www.dropbox.com/s/j5kbwp2p56yti55/list%20buildings.txt?dl=0
There are agb and ags files, these ones don't seem to be described with LOD.
There are only 12 .fac files. You should probably try first on them :
POLYGON_DEF lib/g10/autogen/point_building_60x60_500.fac
POLYGON_DEF lib/g10/autogen/point_building_60x60_120.fac
POLYGON_DEF lib/g10/autogen/point_building_60x60_80.fac
POLYGON_DEF lib/g10/autogen/point_building_30x30_40.fac
POLYGON_DEF lib/g10/autogen/point_building_30x30_32.fac
POLYGON_DEF lib/g10/autogen/point_building_30x30_24.fac
POLYGON_DEF lib/g10/autogen/point_radio_tower_30x30_200.fac
POLYGON_DEF lib/g10/autogen/urban_high_ireg_500.fac
POLYGON_DEF lib/g10/autogen/urban_high_ireg_120.fac
POLYGON_DEF lib/g10/autogen/urban_high_ireg_80.fac
POLYGON_DEF lib/g10/autogen/urban_high_ireg_32.fac
POLYGON_DEF lib/g10/autogen/urban_high_ireg_24.fac
One more time, don't forget to make a backup.