Can I connect a single XWN5001 to an existing Powerline XAV5201/XWN5001 Kit?

Funny, when I talked to Netgear support yesterday, the tech very clearly told me I have to use another XAV5201 attached to the router by ethernet to connect to a second XWN5001.  

The FAQ weblink you provided does indeed show a method, but it specifically calls to connect an "adapter", after labeling in the sketch the XAV as an adapter and the XWN as a WAP.    I suspect I could add another XAV through powerline, but I need another WAP, not another ethernet connection.

I downloaded the Manual and the Installation Guide.  The Installation manual is more clear about the method using the security button method, but I think I will try the second method in the Manual that uses Genie to set the security key first.

I tried using the security button method a few days ago, and I thought I was successful, but none of my other Wi-Fi devices could connect afterwards.  Either than is normal, which means I have to redo the setup on all those devices, or I did something wrong (more likely).   I suspect I pressed the security button wrong and it got stuck down in the groove.  I noticed that when I was resetting the original pair to factory default.  Never try something new late at night!