Windows 10 – How to properly mix 5.1 sound to stereo

I usually watch Blu-Rays with PowerDVD 16. For some time, instead of a monitor and a 5.1 sound system that I used before, I now use a TV via HDMI. The television only has a stereo.

When I had the 5.1 sound system, I usually put the center much higher than the rest to hear the voices correctly.

Now, with television, I can not mix channels at all. PowerDVD or Windows (now do not do it) automatically mix the channels to the stereo in some way. But the voices are too quiet most of the time.

How can I change that? My first instinct was to have a virtual sound device (with 6 channels) where I can customize the mix and the result is sent to the actual sound device. I have not found anything in this.

Through Google I found some things about "AC3Filter" and "ffmpeg" and that those applications are able to mix correctly the sound. But I have not found anything about how this works, only that it should work.

Can anyone explain to me how this works?

PS: I know that PowerDVD probably can not use third-party filters and stuff. So I think VLC or similar players are also possible.