Thanks for the speedy response!
The audioserver is setup and paired with a reliable network connection. Both audio zones play internet radio perfectly.
The stereo connection is powered on the same supply as the audioserver. This photo shows the setup - both LEDs on the stereo extension are permanently on (ie. Green/orange). I believe this indicates an extension that is not yet paired, which makes sense given it won’t pair/show in a tree turbo search.
The audioserver is findable over the network and is running the latest firmware.
Any ideas?