It's been awhile since we've heard this organ, and I've been thinking about doing some "new" Buxtehude, so, here is the first enstallment... :-)
When I did this yesterday, I had just watched a performnace of Monteverdi's "Vespers" and was thinking about the sound of the brass. When I started playing through the "Fuga" I remembered the "special" sounds of the fabulous reeds on this organ! To me, they are THE closest at "imitating" real brass instruments, so...
The "Prelude" is played simply on the Principals 8',4' & 2' of the Rückpositiv. The "Fuga" is played on the Trommet 8' with the Octav 8' of the Oberwerk, with the Pedal playing on the Dulcian 16', Trommet 8', and Octav 8'.
I think you'll find that this makes for a most unusually effective performance. You can ALMOST here the real brass instruments... ;-)