In series with valve which bypasses the boiler at rest (or PAC) is identical to in parallel (except the vocabulary)
sorry but in series c is in series and in parallel c is in parallel
and from two or even 3 receivers or transmitters things get seriously complicated, especially for the regul.
in addition let's stop to think only 3 or 4 way valve, even if they are very useful a lot of priority can do this with the pumps and or non return