It would probably be worth calling Buffalo support on this one, they may know something not in the manual that could help. I believe there is a process to force a firmware install from a usb device but I don't know if that affects passwords or not.
On the bright side I believe your data should be accessible on the drives if you connect them to a PC running Linux. I don't recall if it uses XFS like the earlier models or not but plan to take a look at mine sometime in the near future.
I assume that the passwords are stored in the flash along with the rest of the operating system but I haven't verified that yet.