Uplifting pianos in Ultravox's gripping concert (6)
I believe the answer is:
unison
'concert' is the definition.
(to work in concert is to work in unison)
'uplifting pianos in ultravox's gripping' is the wordplay.
'uplifting' shows that the letters should be reversed in order.
'gripping' says the answer is hidden in the clue (the answer is held or gripped within the clue).
'nosinu' is hidden in the letters of 'pianos in ultravox'.
'nosinu' written backwards gives 'UNISON'.
(Other definitions for unison that I've seen before include "All voices together" , "Voices in complete agreement" , "Concord, sounding or singing together" , "Public service trade union" , "Sounding or singing together at the same pitch" .)