If find in the end you can not get emontx to work for you - you could try instead of emontx you use an emontx shield and wemos r3 ( though I never tried with 3 phase )… and send data to both domoticz and emoncms
use this to install domoticz on your emon PI or whatever you are using
sudo curl -L install.domoticz.com | bash
I’ve done pretty much all that you want too… but using openwrt on a opesource router platform ( BPI-r1) as my base has pretty much everything I want on there for me as an all in one device