After some more searching I found this post which recommended visiting this address http://isy.universal-devices.com/99i/admin.jnlp - and this did the trick. This downloaded admin.jnlp from that location was able to successfully launch the admin console v4.9.0. Whew!
Note: oddly the first time the admin.jlnp file is opened I get a "unable to launch the application" "Error: JAR resources in JNLP file are not signed by the same certificate". The 2nd time the same file is opened it all works fine... the ISY Finder appears and then automagically the login prompt appears and everything appears to work.
