Kauffmann's prelude to "Christe, du Lamm Gottes" is another example of using a chorale melody as a bass line, to create a little trio for organ. The upper voices introduce each phrase of the choral melody with short imitations and play and accompaniment that is nothing more than tha harmonies written out in aigth notes. A usefull trick to master for improvisations.
The recording was done with the Hauptwerk software and the sampleset, made by Voxus, of the Müller organ in the Sint Bavokerk, Haarlem (http://www.voxusorgans.com/en/product/haarlem).
Score available here: http://partitura.org/index.php/georg-friedrich-kauffmann-christe-du-lamm-gottes