I had the same problem with my Helix Rack. The procedure is basically the same as above however as the Rack does not have the same buttons as the floor, to enter the boot mode you need to hold down the ECN1 and ECN6 (The buttons under the LED display) and then switch the Helix Rack on. Make sure HX Edit is not running and then run Line 6 updater. The rest of the procedure is the same as above,
Thanks for the help I would have been totally stuck otherwise!