As for Adorno, his work does not fit in the category of biography. Rather, it is philosophy. Although still in print, it awaits a translation into language. (No, a word is not missing in that sentence.) I suspect that some of the references to his work that one encounters along the way are made by people who have taken him on someone else's say so. If curious enough, go to Amazon.com and read a page or two of his Mahler: A Musical Physiognomy. Then write a paraphrase of what you have read and post it here. 
It's philosophy all right, but also musicology and criticism. Remember Adorno started out as a music student (with Berg and Schoenberg); the foulmouths even say he turned to music and criticism the same way all of them presumably do: as a failed artist. (That's not exactly true. Actually, there's an interesting disc out with Adorno's compositions, which are not bad at all although truly enough highly Bergian and a bit Mahleresque.)
As for paraphrasing Adorno on Mahler (who for him was perhaps the greatest of all composers), can you paraphrase de la Grange, Blaukopf, and the others? Not possible, of course, as there is too much to the man to turn it into a phrase.
But let's let Adorno himself sum up his thoughts on Mahler:
There was, first of all, Mahler's "ability to organize a totality" based on the logic of the "individual figures" that enter into his compositions as their elements, instead of the logic of "an abstract, preordained design." So, without suppressing the individual nature of these elements and subordinating them to some scheme or project or prior notion, he was shaping them into an organic whole: in other words, "starting from the chance nature of existence" (that's those unique and unforced individual figures; it's just Adorno's philosophical baggage speaking here), Mahler "transformed it into a coherent whole, without having to borrow from sources no longer authenticated. This is what defines Mahler as a great composer." This simply means that the "preordained design," which here meant the sonata form and the symphonic approach, was already obsolete back then and could no longer be validated with reference to some historico-philosophical justification or even any "essential" principles arising from the musical logic itself. So Mahler came up with a way to keep composing despite the fact that the means available for composers were no longer "authentic": he made something meaningful or "true" out of what was already meaningless and "false."
That's mostly criticism, with the philosophy coming in now: By the time Mahler was composing, the world had turned into a "lie" (let's just assume for now that this was the case), but Mahler's music, using materials derived from that falsehood, managed to speak the truth about it and not perpetrate what amounted to just another falsehood like most other composers, and in doing so it also succeeded in describing the exact ways in which that world indeed was a lie.
What does that mean, how did he do that? Using a bit more typical language of the Critical Theory, Adorno states that, in Mahler, "the scars of failure are transformed into the bearers of expression and therewith to the fermentation of a second success." Which is simply to restate what I just said above: that at the time Adorno was writing, it seemed like the world had already come to a catastrophic end (what with the Nazism, Holocaust, the war, and the failure of the Left project = the Soviet Union), and in accordance with Adorno's understanding of culture, this failure, like all characteristics of society, was reflected in cultural products as well (this being those "scars"). In his language, culture, too, had become "false" (no longer immediate and "true" as in earlier times, of which a prime example would be Beethoven's 3rd, but that's another story -- it just basically means that earlier on, cultural and societal developments were "at one," with culture kind of being the physiognomy of society, its characteristic mark so to speak -- but no longer so), and Mahler's genious was to be able to take these "damaged" elements belonging to a "false" culture and transform them into something that paradoxially was "true." His music, Adorno explains more musicologically, "inquires how the sonata form can be reconstituted from the inside" (it was not quite the time to entirely abandon it yet), and it does this without doing violence to the "living specificities" existing within this music and constituting it (those "individual figures" above, for instance). This way Mahler's music was more "true" than other composers'; what it represents is "a fully composed-out disintegration and collapse": in other words, he managed to compose the face of the world. (Well, you'd have to accept his diagnosis of the world to see the point in this phrase.) It accurately reflects the world or the society from which it stems forth by abandoning the idea that music should be something affirmative (that makes us feel good about life...); instead, he turned it into "the memory of a past life as a utopia that had never existed" in order to speak more successfully of "a world infinitely full of hope, although not for us."
Nice phrases after all! Each one of them could be a singular paraphrase, but in their original context and in combination they will work better, the way Adorno intended. One such place could be Adorno's essay "Mahler" in his
Quasi una fantasia: Essays on Modern Music which is a bit shorter and more concise, and hopefully still available too. But on the whole the point becomes much clearer if we remember that what Adorno (and many others around him and contemporary to him) was doing was to a large extent influenced by his reaction to the rise of totalitarianism from the early '20s on and to the specific kind of violence it exacted on individuals.
How's that for some Cliffs Notes on why we should listen to Mahler?
PT
