Since I cannot say everything I would like to say, I will start from the beginning: Einaudi.
I don't particularly like Einaudi. And I don't consider him the flagship of post-minimalism. Perhaps Feldman (user) doesn't know it, but I am a great admirer of historical minimalism and many authors and compositions that are in various ways post-minimalist. The "experts" tend to criticize this term, post-minimalism, because for at least 30 years it has served as a catch-all for an infinite series of different styles and research. Well, many of these styles or micro-genres, in my opinion, are now far from the scope of so-called classical music or contemporary classical music. It is art music, "fringe" music, frontier music, but saying that Einaudi was a student of Berio is not enough to include him in a discussion of alternatives to research music.
I don't like the same argument regarding the gap between pop and "classical," because today "pop" is not an alternative to classical. It is an alternative with a tide of different genres, including many subgenres of rock. Is Burzum pop? Is DJ Spooky pop? Is John Zorn pop? None of them do "classical," with the inevitable quotation marks, but that doesn't mean they can be considered popular. The clash between classical and pop is a founding myth of the "classical" musical avant-garde; it is not a problem in itself, it becomes a problem at the moment we pose it as one.
What is being discussed under the surface is not "pop" understood as a musical genre—that is, definable by MUSICAL characteristics—but pop as a dimension of consumption, probably defined by sales percentages or recognition. And here the problem is much broader. Does Mozart sell more or less than Lady Gaga? Well, Mozart HAS SOLD over the years certainly more than Lady Gaga, he is better known (he has had more time to become known) and he will be in the future as well. Does Ivan Fedele sell more or less than Lady Gaga? He certainly sells less, but he has income, he has the possibility to survive and do his job, like everyone else, and if he wanted to enter into a market logic, he would do different things from what he does. And therefore, in a certain sense, he would no longer be Ivan Fedele.
What should Ivan Fedele do to compete with Lady Gaga? Should he do what Einaudi did? And what did Einaudi do to compete with Lady Gaga? From my point of view, Einaudi's possible choices were two: to do what he wanted from an aesthetic point of view and have been "lucky"; or to make commercial choices, in a commercial sense, and go looking for luck. I do not pass value judgments; I am a person who believes deeply in professionalism, and for me, achieving success is not a sin, it is a symptom of well-utilized abilities. But if we are talking about musical popularity in terms of COMMERCIAL popularity, then we exclude a series of styles and genres a priori. We cannot "blame" Xenakis for doing what he liked, and we cannot praise Einaudi for doing what he liked. Combining moral judgment with aesthetic criticism effectively means saying that Xenakis had an obscure reason for making his music (namely, he wanted to kill classical music, as many fools continue to claim) and at the same time claiming that Einaudi also had ulterior motives for writing what he wrote (namely, to make money and become famous).