When I tried to update an individual NKS library then the Product Location location started with three (!) forward slashes ("///Volumes/...") and gave me an invalid Product Location error. There is no longer a button to change it. The download location was on the same external volume, looked ok ("/Volumes/..."), the "Change" button for that was visible and the download worked.
Using "Update All worked with the stored settings, the NKS libraries got installed in the correct place.
However, the .plist files still contain a bad path if the boot volume is named differently from "Macintosh HD" and require manual fixing, this time of 24 files.
See https://forum.vsl.co.at/post/324137 if you have the latter issue and the libraries don't show up in Komplete Kontrol.