I knew it was too good to be true - the "Add Mesh Node" function on my 2927ax fails to find both of my two wired AP960C nodes or the wireless AP960C node.

As the only "supported" AP in the Mesh Support List is the 906 (sic) I thought I'd check that the problem doesn't lie with my 960's - I tried finding a factory reset AP903 on 1.4.6 firmware as a node. No luck with that either.