Now I think I can take this one to an end:
After *borrowing* a WeatherLink installation for Windows I got the additional Channel running on WeatherCat. This is how I did it:
?
Installing WeatherLink on a Windows machine (old Acer Laptop)
? Connecting the USB data logger into the Acer
? Running WeatherLink
? Following the Walkthrough of WeatherLink, and
? within Station Configuration ticked 2nd Temp
?
Cleaning WeatherLink on a Windows machine (because it was only *borrowed*)
This damned Station Configuration (do you notice the *small* differences???) is not available within the MacOS software of WeatherLink.

MacOS:

Windows:

Now, what shall I say? I am really disappointed about Davis...

Cheers,
Reinhard