How can Boulez be a pre-cursor to Schumann?

It is a question of the bias of listening. If we listened --just listened -- we wouldn't need to care about whether a piece of music is tonal, atonal, post-tonal, or pre-tonal. We would simply respond to what we hear; the sounds would have or not have meaning. The experience might be likened to my reading Finnegan's Wake, an experience I enjoyed thoroughly last year and am currently repeating, in fact; but please don't ask me to explain it.

We shouldn't have to know anything at all in order to listen.