I should have been more clear, sorry.
I only connected the Surf Soho to the old router because on its own the Surf Soho will not successfully connect to the cable modem. See attached image.
The WAN interface continues to try to connect without success. I did more searching of the forums and found this: SB6121 Cable Modem which I had hopes for as I have a SB6120 Cable modem, but to no avail.
As soon as I route the Surf Soho through a regular port on my old router, everything works. But it is not a viable solution.
My previous reference to different firmware revision was from this post: Surf Soho WAN will not connect - #18 by avrjeff
Any help would be appreciated.
Thanks,
Mort.