Six trios composed for guest (7)
I believe the answer is:
visitor
'guest' is the definition.
(I've seen this before)
'six trios composed' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'composed' indicates an anagram.
'trios' anagrammed gives 'sitor'.
'vi'+'sitor'='VISITOR'
'for' is the link.
(Other definitions for visitor that I've seen before include "Company" , "One coming calling" , "Guest - tourist" , "She calls" , "who might stay?" .)