Everything extremely audible? Not quite (6)
I believe the answer is:
almost
'not quite' is the definition.
(I've seen this before)
'everything extremely audible?' is the wordplay.
'everything' becomes 'all' (all things).
'extremely' suggests removing the centre (only the extremes of the word are used).
'audible?' becomes 'most' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'all' with its middle taken out is 'al'.
'al'+'most'='ALMOST'
Can you help me to learn more?
(Other definitions for almost that I've seen before include "Virtually" , "Not totally" , "Not entirely" , "Well-nigh" , "Nearly, not quite" .)