In the installer's forum, someone suggested that it worked when putting the Extender output into a Xantech connecting block's OUTPUT, which is to say, by putting 470 ohms in series with the extender output.

The Niles stuff definitely uses different voltages. It is a bad idea to mix Niles with anything unless you drag out the scope, compare voltages...in other words, do something that your installation labor charges will probably not support.