Control of navien tankless system

Hello all, I am in the middle of installing a navian tankless water heater to run a bunch of radiators - since this setup is generally only used in Europe it seems figuring out thermostat control and radiator valve control is actually a pain.

They have their own controller but as far as I can tell has no third party integration:

For the radiators themselves I ordered a few tado smart radiator valves (from the Uk) so that should work on that end

I figured out the hard way nest only works if you buy the uk model which comes with an intermediate controller to make it “opentherm” compatible.

The other option may be a relay based system for controlling the manifold (18 radiators total) this seems overkill and still doesn’t control the tankless system itself

Thoughts / product suggestions appreciated