Tex with duo performing in evening wear (6)
I believe the answer is:
tuxedo
'in evening wear' is the definition.
(I know that evening wear has part(s) of the class the tuxedo)
'tex with duo performing' is the wordplay.
'with' means one lot of letters go next to another.
'performing' indicates anagramming the letters (the letters move around or 'perform').
'tex' after 'duo' is 'duotex'.
'duotex' is an anagram of 'TUXEDO'.
(Other definitions for tuxedo that I've seen before include "American dinner jacket" , "Garment" , "American DJ" , "Dinner jacket (US)" , "An American monkey-suit" .)