1) Color Space:
Rec.709 is recommended as it makes dark areas appear darker due to higher gamma. sRGB appears slightly washed out in comparison, but either standard is fine.

2) Max Brightness:
Max Brightness should be increased all the way, resulting in more detail in bright areas.

3) Min Brightness:
Similarly, Min Brightness should be decreased all the way, resulting in more detail in dark areas. This way, the whole dynamic range (contrast between the brightest and the darkest pixels) is preserved, resulting in more natural graphics.

4) Brightness:
This is the actual brightness setting that should be adjusted as suggested by the description.

5) Comparison:
To demonstrate the difference between dynamic ranges and the color spaces, below are 4 images (JPG, because of the 2 MB file size limit on Steam, but still enough to see the difference) of different dynamic range and color space combinations, all taken with Brightness in the middle.

Rec.709, full dynamic range:

sRGB, full dynamic range:

Rec.709, limited dynamic range (3rd line from Brighter, 3rd line from Darker):

sRGB, limited dynamic range (3rd line from Brighter, 3rd line from Darker):

1) Master Volume, Voice Volume, BGM Volume, Sound Effects Volume and Menu Volume:
These settings are increased all the way by default and should be left as is for the mix to remain balanced as originally intended.

2) Ballistic Impact Volume:
As the previous settings, this should be left as is, but can be changed to Small or Large to make gunshots quieter or louder, respectively.

3) Audio Output Device:
Self-explanatory.

4) Speaker Orientation, Front (L/R), Surround (SL/SR), Surround Back (SBL/SBR):
Self-explanatory. To set up a surround system correctly, see straightforward examples examples below, with more detailed information available in provided PDF files:

https://www.dolby.com/about/support/guide/surround-sound-speaker-setup/

5) 3D Audio:
This option is designed to be used with headphones and makes no audible difference with Windows Sonic for Headphones disabled, but with both features enabled, sound quality is significantly degraded and the "3D" effect is more or less the same as without them since headphones and stereo speakers can only do so much when it comes to the "surround" effect. Generally speaking, disabling all software processing features like this one ensures the highest sound quality.

6) Sound Reverberation:
This option is turned on by default and sounds natural, so it should be left enabled.

https://gtm.steamproxy.vip/stats/2050650/achievements