According to a theory embraced by some contemporary musicians, music is simply a series of sounds, bereft of meaning.
Conclusion (thus)
The music of these contemporary musicians fails to conform to their theory (i.e. the music of these contemporary musicians does have meaning)
Evidence
These musicians encourage audience acceptance by prefacing their performances with explanations of their intentions (since they realize their approach to music is very weird).
Evaluate
"Bereft of" = lacking, devoid of. If we don't know that, we'll struggle to understand what failing to conform with their theory means, although we could make do with thinking,
Where does the author think he establishes that their music has meaning?
The closest semantic cousin would be explanation of their intentions. These experimental musicians who are about to play a bunch of weird noises, since to them, 'music is just a series of sounds with no meaning', first tell there audiences a little disclaimer:
Hey, everyone. Thanks for coming out. We're going to be doing stuff that sounds [smugly] a little different than what you're used to tonight. We believe that music has no meaning and is just a series of sounds, so we want you to listen to what we're doing and accept it via that framework.
Our author is basically saying, .
Goal
Look for a linking answer saying .
But we'll take anything that functionally allows us to prove that the music of these musicians does have meaning.
And if an answer isn't giving us a mechanism to prove that "their music has meaning", then it's functionally worthless to us.