Ok, I've found that. It is not mentioned in the manual.
I am able to use EthernetSettings to set the IP address, listening port and set to "Enabled". (how do you disable it again??)
However, when I go to PLW Recorder, and "settings", then select CM3(ethernet), there is no device to select. (unlike when I select CM3(USB), where I can select a device)
Even if I put in the IP address and listening port down the bottom and hit refresh, there is still no device to select.
Also, how do I enable Power over IP?
Thanks for your help.