Thanks for this quick reply !
Yes I have already a SCSI emulator (PolySCSI from Polykubos / https://www.polykubos.fr/en/accueil/6-16-polyscsi-emulation-stockage-disque-dur.html#/12-kit_polyscsi-polyscsi_assembled_board ) and it works very well with my FM Towns UX20 .
But as you said, FMT-121...