Just rename the sensors to what they represent
To use sensors that are not physically on the Quadro, you need to go to the quadro sensors page and add the NEXT sensors to any of the free software sensor spots of the quadro.
If you do the water-ambient virtual sensor, that's also where you will put it so the quadro can use it on its fan curve.
Trying to control a water cooling system like a house makes little sense in my opinion. In other words, regulating to some kind of difference (water<->environment) or similar.
If then only according to the water temperature. Curve 25 °C .. 38°C ==> 10 .. 100% fan power with a progressive increase.
This differential control ensures that the water temperature is lower in absolute terms in winter than in summer.
However, if the higher water temperature is OK in summer, it should also be OK in winter. With the positive effect that the fans run more slowly and the system is quieter.
First set up a controller that ONLY regulates to the current water temperature and then see if you are happy with it. If something is not working, you can make the control as complex as you like.
Cooling wise it doesn't change much. It's more of a noise thing. Having the fans blasting warm air in summer won't help anyway, so since water temp will vary anyway, might as well not get a noisy PC. All year long, with the same load, it'll be running at the same RPM which is nice. It's more for comfort than cooling really