Depois de horas de busca, deparei com um post nos fóruns da Amped Wireless ( link )
If you know the IP address of the range extender, and you have the vanishing menu because you did not know to disable Auto-DNS, try adding in your HOSTS file an entry like
192.168.5.220 setup.ampedwireless.com # but use YOUR range extender IP address, not this bogus one
save the HOSTS file, and retry accessing setup.ampedwireless.com. Disable Auto-DNS, then delete this line from HOSTS.
There is a Wikipedia article on "hosts (file)" that will help you find where it is on your OS.
No meu caso, e conforme refletido no manual da pergunta original, o IP da Amped Wireless SR10000 é 192.168.1.240 .