Essentially, 'with-it' echoes 'state-of-the-art' (2-4)
I believe the answer is:
hi-tech
'state-of-the-art' is the definition.
(I've seen this in another clue)
'essentially with-it echoes' is the wordplay.
'essentially' indicates the answer is hidden within the clue (essence can mean the inside of something).
'HI-TECH' can be found hidden inside 'with it echoes'.
(Other definitions for hi-tech that I've seen before include "latest devices" , "Involving the latest electronic gadgetry" , "Sophisticated electronics" , "Electronically advanced" , "(Using) the latest developments" .)