There are three stops on this organ that have two positions. Since the sample set maker does not provide an explanation of what each position does, here is my attempt, which I have determined from the church's web page description of the organ.
The first position of the Sexqualter in the Positief draws the 2 2/3 pitch and that the second position adds the 1 3/5 pitch.
The Hauptwerk Mixture is activated in a similar way. The first position activates the unison and fifth sounding ranks. The second position adds thirds.
The first position of the UndaMaris on the Hauptwerk activates the UndaMaris rank and position two adds the Prestant discant. The compass of the Prestant pitches is not identified, perhaps it begins at Middle C, like the Cornet.
One thing not identified on the sample set disposition, but mentioned on the church's description, the Viola di Gamba 8′ is combined with an 8' Roerfluit in the bottom octave.
I did find a demonstration of this instrument. It is a really beautiful sound.
Here is the URL of the demo https://www.youtube.com/watch?v=GJ4nuKw7ItA
Here is the URL of the churches description of the organ https://www.grotekerkvianen.nl/kunst-en-cultuur/historie-en-bezienswaardigheden/orgels/
This is wonderful addition to the Hauptwerk family of instruments.