Piotr Grabrowski offers a beautiful free Hauptwerk sample set of a Mascioni organ, built in 2016 for the Convent Church in Azzio, Italy.
The extension adds the missing C#, extends the pedal compass from 27 to 30 keys (C-f0) and the manual compass from 51 to 56 keys (G-g3). It has a hidden switch (music deck on console screen, see below: the green rectangle indicates the clickable area), which allows to switch between the original and extended version. If the extended version is activated a tiny (Ext) appears on the organ builder plaque.
This extensions works with Hauptwerk 4 and Hauptwerk V.