I have a soundbar since before I bought this TV. It does sound better than the built-in speakers but it started acting up recently (volume going up or down every minute or so for no reason). I tried resetting it, re-flashing it, etc but nothing worked. It doesn't happen always either and I haven't figured out a pattern.
I decided to stop using it and started looking for better soundbars. Eventually I will get a 5.1 or 7.1 system but for the moment the TV speakers are more than acceptable for everything I do - movies, TV, games -- I don't use the TV for music. For now though, the speakers are sufficient. They don't sound too bad. To be fair, there's not much reason they should since there's enough space where they're mounted for decent sized cans.
Surely most people (especially for anyone who is dropping decent money on an OLED) are running external speakers?