Hack probing new line-up of hot rock group (3,3)
I believe the answer is:
the who
'rock group' is the definition.
(I've seen this before)
'hack probing new line-up of hot' is the wordplay.
'hack probing new' becomes 'hew' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'line' indicates putting letters inside.
'up of' is an anagram indicator (I've seen 'up' mean this (letters get chucked up)).
'hot' with letters rearranged gives 'tho'.
'hew' going within 'tho' is 'THE WHO'.
Can you help me to learn more?
(Other definitions for the who that I've seen before include "questionable identity?" , "Pop group (Tommy, Quadrophenia)" , "Tommy, Quadrophenia rock group" , "British pop group" , "Loud rock band" .)