I've tried to get it to enter EM mode as you suggested, without success.
I've also tried the TFTP load procedure, but after I see "accepting requests.." nothing happens - the drive powers up normally. This is on a different PC where I was happy to change the IP address.
NAS Navigator sees the drive, and gets its name right, but claims not to be able to connect to it, and offers to change its IP address. When I say yes, change the IP address, NAS Navigator tries to do so but announces that it's failed. On the NAS Navigator display I see a totally weird IP address, 169.254.163.88. My browser won't connect to that address.
I think I'll just scrap it, and buy different brands in future. This is too tedious for words.