I play a lot of Buxtehude, both the big and small pieces. The Germanic Baroque sample sets I have are Zwolle, Steinkirchen and Zoeblitz. I really love my Steinkirchen! I have found so many beautiful sounds, from the simplest to the most exotic. There are no limits to the variety of sounds you can discover. Often I will take a simple chorale prelude and play it through 3 or 4 times, with different registration. The principals are just lovely, and often 8,4,2 sounds full enough for a pleno without mixture. I often add the 2' flute to the principal chorus, it gives it a special luminosity. For more solidity add the 8' flute. The pedal sounds are beautiful once you get used to them; they are quite different from the manual sounds. In my opinion you can't go wrong with Steinkirchen, you will find variety as you experiment. At first I couldn't find combinations for Bach Trio Sonatas but eventually the solutions revealed themselves. I discovered the use of just the 16' alone in the pedal for quiet pieces, and closing the shutters with a loud accompaniment on the Oberwerk. There is a CD of Martin Bocker playing the real instrument. It sounds fabulous. The first piece is by Scheidemann and sounds like the sounds you want for Buxtehude. Here's the link:
https://www.youtube.com/watch?v=u1ZxJP3f1N8
Now I also love my Zwolle. I recognize that there is controversy about the neo-baroque restoration, but I find the sounds luminous and enveloping. I play a lot with earphones and I have gotten used to the ample acoustic. This is actually my go-to organ for most music. (I have tuned it down to 430, I just like the way it sounds that way…). There is a simplicity about Buxtehude, along with the gravity, which many organs with beautiful pure sounds will render.