I just uploaded the Zen 188.8.131.52 firmware to my 585v7, works just fine and the interface is a bit nicer.
However, the firmware is Zen branded, and not generic so needs a couple of small "tweeks" but nothing terrible.
The set up is slightly different from a factory reset, on the first page you should uncheck the Zen auto configuration.
The local address page is fine.
The public address page needs you to enter your ip address, and where it asks for "public network" you use your ip address followed by /32
That' it, all done. Pics below for clarity.
Ps, Please remember to use the correct password or it won't work!