Interesting what you where saying a while ago Snyprrr about Feldman.
IX and Feldman seem to be a perfect antithesis of each other, making them perfect companions.
Feldman is the abstract ticking of the clock of time, to the man on the street, city and air. Everything happens in a way that is disassociated from this city dweller. Feldman is like an observer (not unlike Cage), and the world is experienced through that personal perspective.
Xenakis, on the other hand is the primal forces of nature that on any day could destroy that figurative city. He is also at the the psychological base of human and animal's being. He is an assimilation of these forces and remains rooted in the pure essence of human being and emotion.
Actually that might make a fascinating thread, "Allegories for composers' philosophies"?