After many trials installer was able to complete the installation
I used the following image (already used before and failed)
http://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/weekly-builds/amd64/iso-cd/firmware-testing-amd64-netinst.iso 11/30/2015 06:59 281m
I had tried different BIOS configurations, and in the scenario when it worked, the last thing I changed in BIOS was an option related to UEFI: "Boot Priority" [UEFI First]
So after system start I had "EFI USB Device (the one whit debian installer) has been blocked by the current security policy."
After pressing ok, debian installer started in Legacy boot mode and all went ok
...but I don't know if it's just a coincidence...