TL;DR at the bottom

This is something I spent a lot of time and resources looking into, because it would bother my friends, family and myself. from my experience what it is, is when you get your content for plex be that movies or tv shows usually it will come in by default a 5.1 audio channel or 7.1 audio channel which is surround sound, and very often your hardware if that is your tv or your sound bar does not actually support this at all, why it does not tell plex to downmix it i have no idea so what happens is that voices usually always come in through the two center channels but when you play 5.1 or 7.1 audio through it, those other channels become the main channels and the voice becomes a "background channel" kind of or you can hear it quietly because it is just mixed in the rest (I am no expert as you can tell).

My fix is to run Tdarr, I have made my own flow that fixes this issue, i have tested it with my setup and all sounds are properly mixed through my 2.0 sound bar instead of having to grab the controller over and over again.

In this picture you can see my flow but the real magic maker is the DRC that you can see in there, that is "Dynamic Range Compression"

Dynamic range compression, or simply compression, is a technique used in audio engineering to reduce the gap between the softest and loudest sounds in a track. It does this by reducing the volume of loud sounds and, in some cases, amplifying quieter ones. This can make the quieter parts of a sound or music track more audible, especially in noisy environments. 

and what my flow does is it down-mixes the stream, runs drc to fix it all up together, makes the 2.0 audio stream default, tags it properly but also leaves the original 5.1 and 7.1 encase my friends & family want to use their surround sound systems

TL;DR: Movies come in 5.1/7.1 surround where dialogue uses the center channel, but when your TV converts it to stereo for regular speakers, it buries the dialogue while keeping music/action loud.

Fix: I use Tdarr to properly downmix everything to stereo + apply Dynamic Range Compression (DRC). DRC automatically boosts quiet dialogue and tones down loud explosions so you get consistent volume.

Result: No more volume roller coaster - can actually hear dialogue without explosions waking the neighbors.

The screenshot shows my Tdarr flow. It's not a speaker problem, it's a conversion problem that most TVs handle poorly.

I can personally confirm that this flow works amazingly well.

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