I haven't played it, but with the console built into the case with the organ mostly above and in front of you, but with the Rugwerk behind you and opening away from you through its case wall, you could suppose the Rugwerk might sound diffuse to distant and mostly be heard from your back speakers, while you might hear the other 3 divisions as a mix of direct and diffuse from your front speakers, with a longer rear reverb played softer on your back speakers.
Just speculation...