I managed to find two old-ish TP-Link MC200CMs with cable and power supplies for £11 on eBay, and I think it might be the best SQ improvement I've ever made (even better than the speakers' Gaias). The bass definition, dynamics and transparency have all gone up a level.
At the moment I have a 30cm Sotm dCBL-CAT7u ethernet into the Zenith. I'll play around with different ethernet cables, and maybe reintroduce the Sotm ISOCAT7. I've also got an Ifi iPower X on order for the 2nd MC200CM.
But wow! Exciting times. I can't see myself not trying a Sonore opticalModule when it becomes available again.