I spoke to Vaillant about using a 3 zone valve and they say that it won't be able to transmit more than 20 Kw and I'm using a 37 Kw boiler, but that a switching relay to convert the two signals to one signal will work using the VR65 / 470f.
this is correct, but the cylinder coil ratings will only be about 16 kws each.
You can range rate the boiler down for hot water if you use vaillants controls, such as the vr 65
I have several VR65s with with the heating terminals controlling two two port valves... when I first did this I got some figures saying that as the valves pull so little it would be fine...and indeed it is!