3-way - no technical notes. I now know that this has four ports,
two of them inputs, one to be blanked, and two outputs.

5-way - no technical notes. I now know that this has five ports,
two of them inputs, one to be blanked, and three outputs.

Just guessing here, but are the "3 way" and "5 way" also mixers, so would
normally have a hot and cold inlet, which isn't required because of the
external thermostatic mixer?

Christian.