A Rigorous Approach to the Algorithmic Composition of Iannis Xenakis(2009) [pdf]

You only need to make it 40 or 50 pages before Formalized Music comes up. I am not sure I would say they are about the same subject; Formalized Music is about single aspects of Xenakis' music, it is gear talk for the computer musician and gives little insight into his music and method as a whole. They are related but offer very different things.

It has been a surprisingly informative and interesting work so far and is almost what I had wanted out of Formalized Music when I first picked it up all those years ago. Despite being his dissertation and very much written in that style, it is quite readable, the author writing it in his second language helps a great deal; the limitations that English imposes on him result in him explaining things which normally would not be explained in such a work. If memory serves this was part of his reason for writing it in English, he covers his reasons in the introduction but I don't quite remember if that was one of them or just something I noticed. I am about 100 pages in and have not once needed to go into a citation to figure out what he is talking about.