One introducing music reading out two letters (6)
I believe the answer is:
deejay
'one introducing music' is the definition.
'two letters' is the wordplay.
'two letters' can mean two substitutions for 'letter'.
'letter' becomes 'dee'.
'letter' becomes 'jay' (I can't explain this - if you can you should give a lot more credence to this answer).
'dee'+'jay'='DEEJAY'
'reading out' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
(Other definitions for deejay that I've seen before include "Disc jockey (colloq.)" , "player of many tunes" , "Record spinner" , "Record-spinner" , "provider of music" .)