I have been reading Michael Beil’s article ‘Material Shift‘, which can be found in Musical Material Today edited by Claus-Steffen Mahnkopf, Frank Cox, and Wolfram Schurig. The following is by no means an exhaustive review of Beil’s text, but a collection of points which resonate with my current research. I highly recommend reading the whole book, details of which can be found here.
The article is interesting in that it presents a particular perspective on defining ‘material’ in musical composition (something which is not straightforward in general). According to Beil, it is the meaning of ‘material’ which takes precedence over the actual ‘material’ (which is defined as ‘building elements’ in this instance). Beil writes:
‘I can no longer consider material primarily a reservoir of building elements within an organized structure of sounds. In my view, its important properties for composition lie in the medial domain; this makes the material a means, not an end in itself.’ 
As such, Beil’s compositional approach focuses on strategies, communication, meanings and sonic effects. For instance, he writes that he does not ‘consider a quotation to be material […], but rather the act of quotation.’  As such, the actual quotation itself plays a secondary role to a strategy. According to Beil, one has worked in the right way if the quotation is quickly forgotten after it has been recognized (without wanting to quote too much of Beil’s article, pages 9-10 explain this in more detail).
To illustrate his perspective, Beil refers to three examples of his own work: Doppel (two pianos, live audio, live video); Die Zwei (flute, piano, tape, video); BLACKJACK (17 players, live audio, live video) which can be found on his website (links provided).
Beil makes several more interesting points about the reception of his music. He writes that:
‘A second honest colleague found the material in Doppel traditional; while listening, he concentrated on the material as a building element […] [,] as belonging to conservative or deliberately pleasant music. His reaction, however, highlights another important point: it is very difficult for trained listeners to react to music outside of their customary routines. This means that New Music, a music that was originally meant to stimulate reflection on music, is now preventing that very reflection among some of its specialists.’ 
I think this last quote provides an interesting point. Having experimented with traditional idioms in my own compositions, I find that they are difficult to be ignored as such within the context of ‘New Music’. Rather than being viewed as an open space of sounds and frequencies, such compositions are typically interpreted as containing quotation and/or alluding to other musical idioms. This isn’t necessarily always restrictive to the compositional process; however, it is often a talking point amidst the reception.
 Michael Beil, ‘Material Shift’ in Musical Material Today, ed. by Claus-Steffen Mahnkopf, Frank Cox, and Wolfram Schurig (Hofheim: Wolke, 2012), pp. 9-20 (p. 9)
 Ibid., p. 12