My translation of that 'Giomenese': "The buggy custom fw won't allow flashing via usb in many cases". [Therefore you are unable to use updater.exe to change either the fw or basemap, right?].

Before you play Pontius Pilate and wash your hands of this matter, how about try this for an experiment: The unit only allows one map in microSD named gmapsupp.img, correct? So combine the Bluechart with an Atlantic basemap using GMapTool and see if the contours show.