The headphone jack will usually cut the TV speakers off. The jack could be modified not to do this. Requires one wire to be soldered across the jack so plugging in doesn't disconnect the TV speakers. Getting to the jack might be a pain though. A tech could do it for you. Might void the warranty.
If the digital output works with the TV speakers on then you can use them at the same time.
The TV has a headphone jack so you can use that with self powered speakers.
The TV has a coax digital audio output so you can use that with any powered speakers with that input.
You can connect a bluetooth transmitter to either of the above and use bluetooth speakers.