Can't see A1084 AirPort Express behind A1354 AirPort Extreme Can anyone please make any suggestions...? (Preferably, step by step instructions to resolve this issue).

I am using AirPort Utility 6.3.2 on a MacBook Pro running MacOS X 10.9.1 Mavericks.  AirPort Utility suddenly can't see my two A1084 AirPort Express base stations behind my A1354 AirPort Extreme (which is running Firmware version 7.6.4).  The Extreme is behind a CenturyLink Actiontec C1000A DSL modem, which is connected to the Internet.

If I use AirPort Utility set the Extreme to "DHCP and NAT," the utility shows that the Extreme has "Double NAT."  



If I set the Extreme to "Bridge Mode," that issue resolves.  



But, in neither case can I see the AirPort Express base stations.  

There is a control to disable NAT in the Actiontec C1000A DSL modem's admin panel, but an attempt to make that change doesn't "take" when I click on "Apply").



Because the AirPort Express units are old, only the old AirPort Utility (v5.x) can be used to configure them - but, that old version does not run under Mavericks.
I cannot comment your post, but at least I have a suggestion: Download a copy of Airport Utility 5.6 working with Mavericks here.

Edit: it seems to me your network is working as always (at least before you began fiddling...:-)), but the thing is you updated Airport Utility to the newest version and therefore cannot see the Expresses? This is a "feature" of the newest Airport Utility.