It would have to sit between your source(s) and TV and decrypt/recrypt the audio in realtime -- which means it would need to support the various codecs in use today.
Would be easier to buy external speakers and wire it up with those.
If your tv is the thing generating the inaudible signals, it could still choose to play them using its internal speakers, and send just the 'real' audio to the external ones.
Would be easier to buy external speakers and wire it up with those.