I dismantled many TVs for parts and gave away or dumped a lot of speakers from inside.
Samsung, JVC, Panasonic, Sony - all had internal speakers connected via connectors very similar (not nessesarily compatible) to PC FAN connectors.
Unplug TV, unscrew back cover, do not touch main power board straight away. High Voltage dissipates through bleeding resistors in a few minutes.
Trace usually white/red wires going from speakers to one of the boards. Cut in a convenient place.
Connect wires from the board to the external wires going to external speakers. You may use DIY interconnector somewhere on the side. Those connectors for connecting external Speakers can be bought in Jaycar/Surplustronics or salvaged from old amplifiers.
10W output per channel many TV have is enough to drive good quality external speakers.