I am finding this so tough that I am not even sure what questions to ask that might unlock it for me. So here goes and if providing hints is too revealing without spoiling it for other solvers, I will put the crossword aside until the answers are published.
Which squares have clashes? I think 10,14.19, the intersection of 39d and 44a, perhaps 31 and 17. So I assume that there are 5 others.
I assume that the letters in the clashing cells contribute to pieces of work by a famous composer. I have no idea about these, so generous hints will be welcome.
Might 1a be "above". If so, why? If not, a hint is welcome.
A big hint for 36d might help me to get restarted.
It certainly looks as though Schadenfreude's farewell listener is a classic.