I can't resist jumping in here, even though I am completely unqualified to comment on the "realism" of the Bovenkirk. I purchased Vol I and II together, and III a few days later (along with more memory!), and I've sensed no difference in quality between the various stops. Even with the newer, much higher quality headphones that I bought last week. Yes, different stops have different presence and ambience, but this is what I'd expect from a reasonable listening position in a church, and is consistent with the various recordings I have.
What I really want to say is that I'm absolutely obsessed with the Bovenkirk. As I've told Brett privately, I spend much of my day thinking about what I'll do with it, and stay up way too late playing it

. It's a fantastic instrument and I can't recommend it too highly. All of it.
Like Eric, I was greatly moved by Brett's recording of BWV565 in the Vol I demo section, and this alone is the reason I took the plunge and bought the Bovenkirk (as well as purchased Hauptwerk!).
Anyway, that's my relatively uninformed opinion. I may not know organs as well as many of you, but I know what I like
steve