Big orchestral piece provides a clue to one such former musician (6)
I believe the answer is:
prince
'former musician' is the definition.
(deceased American musician)
I don't understand the remainder of the clue.
(Other definitions for prince that I've seen before include "Canadian province" , "Senior male member of a royal family after the sovereign" , "King's son" , "Son of a royal house" , "He's a royal" .)