You are right in telling me that Metastaseis
has a conception of material different from that of Webern for instance.
One of the most famous examples, amply documented by Xenakis himself in his first chapter of Formalized Music, concerns the conception of the Philips Pavilion and his first major orchestral work, Metastaseis
One can cite such works as Metastaseis
or Pithoprakta in which he successfully applied this method (Xenakis 1963).
13) One of the icons of twentieth-century architecture, the Philips Pavilion for the World Fair in Brussels in 1958, (14) composed of hyperbolic paraboloids, was developed by Xenakis in parallel to his musical research that resulted in his first major orchestral composition, Metastaseis
Xenak is had already developed this concept of music in his orchestral works Metastaseis
(1953-4) and pithoprakta (1955-6), before his electroacoustic experience--his first electroacousitc piece is Diamorphoses (1957).