The part people get wrong
Power Is Not the Same as HDMI
This is where most DIY jobs and a fair number of cheap installs go wrong.
HDMI, optical, ethernet and speaker cable are all low-voltage. They are allowed inside a wall and there is nothing complicated about routing them properly. Power is a different question with a different answer.
The power cord moulded onto your TV is not rated to sit inside a wall cavity. Running it through the wall is a genuine fire risk, it fails inspection, and it can void your home insurance if it ever matters. We have found it behind a fair few walls we have opened up.
The correct fix is an in-wall-rated power kit: a recessed outlet behind the TV, fed from your existing outlet through cable that is rated for the wall. Your TV plugs into that. Where a kit is not appropriate we bring the power out to the existing outlet and run a raceway. What we do not do is bury a cord and hope.
Can you hide the soundbar and cable box wires too?
Yes. HDMI, optical, ethernet and speaker cable are all low-voltage, so they can run inside the wall alongside the TV’s own cables, and in-wall concealment starts at $99.99 on regular drywall. Power is the exception: it needs an in-wall-rated kit or a raceway to your existing outlet, never a buried cord.