Six tours organised with opera's principal star performer (8)
I believe the answer is:
Here is my best explanation:
'star performer' is the definition.
'virtuoso' can be an answer for 'performer' (thesaurus). I'm not sure about the 'star' bit.
'six tours organised with opera's principal' is the wordplay.
'six' becomes 'vi' ('vi' can be a synonym of 'six').
'organised with' indicates an anagram.
'principal' says to take the initial letters.
The initial letter of 'operas' is 'o'.
'tours' with its letters mixed up with 'o' can make 'rtuoso'.
(Other definitions for virtuoso that I've seen before include "Brilliant -- prodigy", "A consummate master of technique and artistry on a musical instrument", "Dazzlingly skilled musician", "maestro?", "Musician of the highest technical skill", "Highly-skilled performer", "Maven", "Musician with exceptional technique", "Genius" and "Great player".)