Soup-mix makes musical work (4)
I believe the answer is:
opus
'musical work' is the definition.
(synonyms)
'soup-mix' is the wordplay.
'mix' is an anagram indicator.
'soup' is an anagram of 'OPUS'.
'makes' is the link.
(Other definitions for opus that I've seen before include "Musical composition in the soup" , "Work of 25 perhaps" , "Composition - magnum __" , "Work or composition, usually musical" , "Soup (anag.)" .)