Wouldn't it be easier to leave your SH as a router/DHCP and configure the netgear as an access point to the same network??
Couldn't get it to work - but having 2 x wifi works Ok - range of netgear far superior.
I think the issue you're running into is double natting, but I could be wrong. Either way, I'd recommend the above config unless there's a specific reason you want to keep them separate?
Can you explain double natting - having 2 x DCHP is Ok as long as different IP ranges?
BUT it worked last week - will shut it all down tonight with some hard resets and try again then
Till tommorow . . . . .