@mdvrk The Duo is a slightly different beast and so the technique may not work the same way or may be likely to brick your NAS. With a single disk MCH you have to take the disk out of the enclosure, plug it into a linux system, mount it and hack the files to enable root logon. Then put it back and connect the USB terminal cable. With a Duo there is probably (I’m guessing here) another layer of firmware that is mirroring the disks.
The UART (Serial to USB) connection in the past didn’t have any password to login. That’s changed in the recent firmware upgrade, I guess. I wonder if anyone knows the passord.