As Andrew says, you should be using the TV on the monitor output of the Denon. You should not attempt to pass signals through the TV to the Denon, nor should you try to "stream" directly to the TV over the network as you've been trying.
The reason for this is that the TV does not support many of the audio formats your Denon does, and will mangle or block them. Likewise many video formats need to be converted into something digestible by the LG.
Best practice is to route everything directly to the Denon, and it will then pass the video through to the TV while outputting the sound itself.
If you cannot run HDMI from the PC to the Denon (perhaps it's in another room or something) then if you have to fall back to using the network you will have to get DLNA working and get used to the idea that you will not get "untouched" audio from your movies as you were hoping for.
I just responded to another thread recently with a user trying to stream DLNA to their LG C9 OLED, and I gave them the lowdown on that. You might want to read it.
Good luck...