Old airport express extending virgin superhub 2
I have the current Virgin Media SuperHub 2 (first available late 2014, I think) and a very old Airport Express (from possibly 2006) and I would like to use the Airport Express to extend my SuperHub's wireless throughout my house, at it gets a bit weak in some places. I have managed to get the Airport Express to provide internet through the SuperHub and to share a set of speakers. This is only because it is wired into the SuperHub with an ethernet cable and configured using the legacy AirPort Utility from here: http://coreyjmahler.com/2013/10/24/airport-utility-5-6-1-on-os-x-10-9-mavericks/
Of course, what I would like is to properly extend my SuperHub's wifi without cables, but the Airport Express (as seen in the utility) can't seem to see the SuperHub's wifi networks. Here is what it shows when I try to "Extend the range of my ... network":
Does anyone know what I should do to get the SuperHub's WiFi visible in the Airport Express's list of networks or if I can manually configure it? The SuperHub security is set to WPA Auto - so I'm not sure what security setting to use when manually configuring the Airport Express.
MacBook Pro, OS X Mavericks (10.9.4)