I have not been able to install the Stiehr-Mockers organ package using the Hauptwerk v3 software. The sample as downloaded is not recognised by HW v3, and includes .ORGAN files which I've net seen on other samples. (I only have used version 3 of the HW software). Could you please indicate if there is a solution for this.
I wish you every success with this project and in recording some of the wonderful organs in Alsace region.