New 802.11n Airport Express won't ...

I recently replaced one dead of two b/g AX on a AirTunes/WDS enabled Airport system comprised of a 802.11b/g Airport Extreme router, two b/g and one 802.11n AX bases, with a new 802.11n AX. The three AX were all added to join the network as relay Airtunes bases, not on WDS, to three audio system locations

When I added the first 802.11n AX it was a simple matter setting it up in the Airport Admin (AA). This new 802.11n, however, will not read in AA when scanned for set-up to configure, and I get a blocking message saying that the Airport Extreme router will not support software/firmware updates for this AX when I attempt to add it as a client after enabling WDS on the system. I can work around the message in settings for security conformity, etc., but then updating goes through the motions without success.

After hard reset, the AX will show up in the Airport Set-up Assistant to configure, and also as a new and separate network in the Internet Connect pane, and AA if I select it as a network, but using either to attempt configuration fails. (A dozen attempts, since persistence sometimes matters with things Airport.)

Since I had no issue with adding the first 802.11n AX to an old b/g system, I can't figure why this one is not allowing a normal read in AA and giving a software grief message on work arounds'.

Still running fully updated 10.4.11. Any thoughts?

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