Producer's question over millions invested in sound being insufficient (7)
I believe the answer is:
showman
'producer's' is the definition.
(synonyms)
'in sound being insufficient' is the wordplay.
'in' indicates putting letters inside.
'sound' becomes 'shown' (I can't explain this - if you can you should give a lot more credence to this answer).
'being' becomes 'man' (human being).
'insufficient' means to remove the last letter.
'man' with its final letter removed is 'ma'.
'shown' placed around 'ma' is 'SHOWMAN'.
'question over millions invested' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for showman that I've seen before include "Person helping to present" , "Circus or fair manager" , "Entertainer" , "Impresario" , "Circus proprietor" .)