Version 5.4.2 was posted in June yes, but 5.4.1 was up in March, and 5.3.1 was up there in March of 2008, both stating support for your N based Extreme. The other links were for the older G based Express and Extreme, and the last link was for the really old B stations.

This does confirm needing the disc up till 5.1 though. No idea about 5.2 as I can't find a download for it anymore.