Finally I managed to use icons .bmp and excel .csv files from TThaven to create an .gpi file with POI Loader.
Nevertheless, all attemps to associate either a .wav file or a MP3 file with .bmp and .csv failed : it looks as if Montana is unable to read .wav files.
I tried to use both sox.exe files :the normal one and the one you modified. When I ran POI loader with yours, sox.exe didn't open while with normal one sox.exe could be run but apparently did nothing.
Fortunatly, alarm can be activated on Montana before each dangerous zone thanks to POI Loader using it in manual mode.