Ambitious chamber music (6)
I believe the answer is:
nonets
'ambitious chamber music' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nonets that I've seen before include "musical pieces" , "Compositions for nine players" , "Compositions for nine performers" , "Groups of nine musicians" , "Pieces of music for nine instruments or voices" .)