If can Help someone :
the idea was to DOWNGRADE or FORCE firmware update.
For QU-SB, this is the way :
1 – QU-SB switch OFF.
2 – Plug the USB Key with appropriate Firmware.
3 – Push and HOLD the FIRMWARE UPDATE Button
4 – Switch ON the QU-SB
5 – Release the Button and wait until the green light.
tips: watch the USB KEY Yellow LED, it should be ON and kind of blinking, showing some activities.
It should upload the firmware, whatever is the version…
Cheers