Hello Martin. Ho Ho Ho.
I'm still on vacation, but I thought I'd drop in and see how things are progressing on this forum. Can you try lowering the HW output to a value of 30 or 35%? See if you get similar results. It could also be an audio card issue as well. Does the Audigy have an option for buffer adjustment? The Buzard samples are a bit more "hot" than the St. Annes, so it would take a lesser amount of stops together to reach the same amplitude as having many stops engaged in the St. Annes organ. I would think that an 8,4,2 combination shouldn't cause any problems with overload however. Also since you have 1 GB of RAM I would personally load the samples in stereo as the Buzard requires only 478 MB of memory! Perhaps for some reason loading in mono is creating problems? I'd also play around with various latency settings as well and see if that solves the issue.
I don't have access to loading the Buzard while on vacation, so I can't try things out yet for you. So, please let me know if these things help or not. Thank you.