Reger - Ein feste Burg ist unser Gott
The organ survived WWII (the cathedral was hit in 1940 and 1944, and for several years had no roof!) and is a unique testimony to the great art of late romantic organ building in Germany.
Max Reger's large-scale choral fantasies have been composed with this kind of instrument in mind, and work perfectly (even though the registration does require a lot of planning and an excellent assistant!) as you can hear in the live recording.
The seamless crescendo from barely...
Wagner - Pilgrim's Chorus
Mendelssohn-Bartholdy - Sonata No. 3
...audible flutes to a thunderous tutti can be experienced in Richard Wagner's Pilgrim's Chorus in Liszt's version for the organ - which adds a truly celestial ending on the 4' Flute!
Felix Mendelssohn-Bartholdy's Sonata No. 3 was composed much earlier, and organs during his lifetime were definitely very different. The long crescendo that he requests in the B part of the first movement is easily and convincingly executed with the Walze, and the second mvt. allows for a comparison of the beautiful flutes and strings of the instrument.
Recordings of two works by Bach arranged by Reger and Liszt are available here.
Pictures of the organ, the cathedral, and the view from the dome are available here.
Stoplist of the Sauer organ here.