Ringers with excellent musical technique (6-8)

I believe the answer is:

double-stopping

'musical technique' is the definition.
(technique for playing a string instrument)

'ringers with excellent' is the wordplay.
'ringers' becomes 'doubles' (a dead ringer can mean a lookalike or double).
'with' says to put letters next to each other.
'excellent' becomes 'topping' (I've seen this before).
'doubles'+'topping'='DOUBLE-STOPPING'

(Another definition for double-stopping that I've seen is " Playing on two strings at once".)

I've seen this clue in The Guardian.

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