Ok, a little progress. I reflashed the card and started again, this time never connecting to network by cable. Now my rPi3 max2play DOES report it has an internet connection (over Wi-fi) 🙂
However I still cannot get AirPlay to work. When I look at which plugins are active (via squeeze server web admin) sharetunes2 is unticked and marked “Plugin failed to load”. How can I fix this? I thought max2play was supposed to be robust and easy to use??