That would just dandy if consoles weren't an issue. I'm planning on hooking up a PS4 and Nintendo Switch to the monitor so having audio output on it is a general fix.
I'm wondering if a 5.1 sound bar setup is actually possible through a headphone jack. Also, I'm an Overwatch player with a 1080 Nvidia card so that LG model was a big no for me, although ultrawide is tempting.
Sound bars probably wont come with DP, but some come with HDMI. I don't know about a headphone jack, but you could probably get a switch to make it work with an optical audio. But really, for your use case, I think it is a bad idea to get a monitor without speakers. There are tons of good monitors out there, just pick another one.
And yes, 21:9 is awesome. HOTS does support 21:9 and you will be able to see more of the field. Once you go to widescreen, you cant go back.
I'll admit I don't have much experience with soundbars however it appears you can connect it to the monitor via USB and then control the volume with the controller that comes with the soundbar or on the soundbar itself.