Many thanks to @bottletop
for the eBay link. I finally got round to ordering the Edimax on Sunday, it arrived yesterday (Thursday).
As noted on the eBay listing, it comes as a bare unit with no cables or manual. The manual is readily available on the Edimax website.
After a bit of messing around with the config to get the device into Infrastructure mode & then get the WiFi credentials sorted, it now works really well. The Edimax does not get a DHCP IP address while in Infrastructure mode, so if you want to change or look at the config, you either need to access the device using it's default IP or change the device's static IP to something outside of your normal DHCP range but within your LAN subnet.
After setting up the Edimax using my Laptop, I plugged it into the Humax, using power from the rear USB socket that's underneath the RJ45 Ethernet socket. The Humax powers the USB when it's online and gets the IP Address via DHCP, after that access to the main web page is possible.
Curiously, the network settings page on the Foxsat shows some odd DNS servers:
Via the DHCP setting it shows 220.127.116.11 (University of North Carolina)
Via the manual settings page 18.104.22.168 (AT&T Services, Inc.)
I'm fairly sure that my DHCP server does not give out either of those addresses, but I'm not overly worried.