I have friends with soundbars for TVs, and heard a few (albeit in shops), and while they are far better than TV speakers, I can't say I thought even the pricey ones were good.
I had 5.1 AVRs in the past but they were terrible for normal stereo music, but they have got a lot better - and more expensive. I make do for multi channel sound on videos with the stereo PCM that my TV generates into my streamer. AFAIK, the mix down to stereo usually follows a fixed formula of so many percent from each of the channels, and I've not come across a TV that lets you adjust that mix...
I often find the dialogue muddy or drowned out by background noise on films in particular. My local TV (FreeSat & FreeView) always seems to have clear dialogue as its audio transmitted in stereo - although I have not verified that. Maybe their mixdown for multi-channel sources is a lot more sophisticated? American films are the worst - maybe dialogue is less important in US, or maybe the most popular actors like to mumble, or maybe I'm culturally conditioned to tune in better to other accents. Curiously, French & German films seem to have clear dialogue like British films do, even if it's all multichannel. Who knows?
Anyway my stereo is crystal clear - to my ears, so I did some tests on ripped videos that had poor multi-channel audio. I put together scripts that processed the audio in ffmpeg, and tried varying the percentages of how much from each channel to use for a stereo mixdown. A fun rathole to slither down on a wet sunday. I did find I could improve dialogue intelligibility quite a bit. Stereo EQ didn't help much in my case.
My conclusion was that while the source can definitely be poor (even a good AV system may not be enough), some of the intelligibility is lost, in my case, by the stereo mix-down. Having satisfied myself I'm not too deaf or loony yet, I now leave it be, and accept some films are a bit difficult. If I was to do an improvement, it'd be to buy a cheap AV amp and basic centre and rear speakers, but keep my main stereo amp and speakers (and subs) to play the L & R channels (this keeping the music playback the same as I enjoy now).