Hello Mark,
When I look at his web site, I have to wonder about how active this project is. Two things stand out: (1) the site (in English at least) does not appear to have been updated since 2004; (2) there is no statement about HW2 support.
I did speak to Ariaan about it a few months ago, and he is very busy with other non organ-related work at the moment, but he told me that he does have a Hauptwerk v2 port of the sample set which he will release later in the year when he has some time.
On the subject of the tremulant, I would guess that there is some sort of default model in HW2 that gives this result. I don't know what it would take to alter the model.
Since v1 organ definition files don't have all of the necessary parameters to control v2's tremulant model fully, basic defaults are used for the remainder, which sound better with some ranks than others. A native v2 port (or the CODM) can always give much better results. The main aim of the v1 import facility is to allow the remaining v1 sample sets to be used in v2 (and to sound better than in v1) whilst awaiting native v2 ports.
Unless there are actually any specific bugs or problems with the v1 import mechanism, there are no intentions to develop it further since it is for backward compatibility only. Development of any new sample sets or organ definitions should use the native v2 formats (full or CODM). I appreciate that some people find the full v2 organ definition format too complex, and the CODM format too simple and inflexible, which we'll attempt to address by making the CODM much more flexible, whilst still keeping it very easy to use, in the near future.
Best regards,
Martin.