Create Roaming Network Behind an NVG599 with Apple Airport Extreme

I want to create a roaming network in my house to distribute wifi to areas not covered by the wifi from the RG NVG599.  My solution is to connect the Apple Airport Extreme to an ethernet switch in the attic that distributes the same ethernet to two other set top boxes. The attic is an ideal location for the second wifi access point. My goal is to allow a device to connect to either the downstairs RG or the uptairs AE using the same SSID and password.

I have put the AE into "bridge mode" and have set the wifi SSID and password identically as the ones for the RG.  However, the internet performs very poorly (or not at all) for the connections to the AE.  I suspect that it has to do with the IP Passthrough settings (currently set to off), but I am not sure what those settings should be.

As a test, I changed to the AE out of the bridge mode to share a public IP address.  The internet works fine, but the network functionality is lost as the AE now sets it own IP addresses and does not "see" the rest of the network.  An error code is displayed on the AE indicating that it needs to be changed to the bridged mode.

Recommendations and questions are greatly appreciated.