>Is sample-based, or does it do some kind of modeling to produce the sound?
 
I'll answer my earlier question.  This thing weighs in at under 1400KB.  If it were sample-based, the samples would have to be pretty skimpy.  Plus there's no additional files, just the one .ens file.  I don't know Reaktor well enough to say that proves there are no samples, but everything points to this doing sound via modeling.

I hope y'all are making a donation to this guy! I just spent a wonderful hour on that page. There are some truly beautiful ensembles there. As if the synths and instruments weren't good enough, the effects blew me away as well. Such incredible delays and reverbs. I made a real pig of myself and downloaded the lot, then made a donation. Of course it helps that most of his audio demos are very nice, in fact there's some beautiful playing on them. Nothing like a good demo to make you reach for that download button. 
 
I have to say, Reaktor has paid for itself many times over with so many wonderful free synths and effects to be had.