Mark,
You mentioned that these are probably "lightly" composed pieces,
meaning that they are more than likely just a basic melody that the
musicians are invited to use for improvisation. I listened to a number
of the tracks and they do sound improvised. I have to wonder, though.
You have probably heard John Zorn's "Game Pieces": A set of strategies
that tell the musicians really specific things that he or she is
supposed to do, based on various things going on between the musicians.
Those pieces often have radical shifts in style and tempo, based on
the system determined by the "game."
Several years ago (I think it was in 1990) I was on a CD that Zorn
also appeared on. It was titled "(Y)Earbook, Vol. 2." That CD
included one of Zorn's "Game Pieces" and it sounded very similar to the
things that Koby Israelite played in the "Angel" series. Both projects
have radical shifts in style and tempo, like the soundtrack to a
post-modern cartoon.
So, maybe these are pieces based on really specific strategies,
rather than just vague melodies on which the musicians are invited to
improvise as they wish.