The most common and most likely answer to this crossword clue is the 8 letter word CHORUSED
I've seen this crossword clue in Financial Times
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More clues leading to the result CHORUSED
Buddy explains!

The straight part
We know that "Sang in service/musical combination" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sang in service/musical combination = chorused.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CHORUSED mean?
CHORUSED verb- To sing or recite in chorus.
- To say in unison; to express in unison.
- To echo (a particular sentiment).
- To sing the chorus (of a song).
- To speak as if in chorus (about something).
- To echo in unison another person's words.
- (of animals) To make their cry together.