String player united a couple of quintets to appear in catalogue (8)
I believe the answer is:
lutenist
'string player' is the definition.
(someone playing a lute)
'united a couple of quintets to appear in catalogue' is the wordplay.
'united' becomes 'U' (abbreviation as in Man U for Manchester United).
'a couple of quintets' becomes 'ten' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to appear in' is an insertion indicator.
'catalogue' becomes 'list' (a catalogue is a list of items).
'u'+'ten'='uten'
'uten' put inside 'list' is 'LUTENIST'.
Can you help me to learn more?
(Other definitions for lutenist that I've seen before include "Plucky player" , "Stringed instrument player" , "Stringed-instrument player" , "Instrumentalist" .)