I am exactly not sure how the CompressorSoundEffect | Roblox Creator Documentation works, i tried to fiddle with the values and managed to get some results, however loud audios are still extremely loud.
What I would like to achieve is cap the max sound at a certain volume.
Not really possible, the way this works is by decreasing the louder parts of the audio and increasing the quieter parts, basically creating an even volume for audio.
That makes audios with high volume still loud.
I managed to get a fairly good working solution with a CompressorSoundEffect with these properties
The loudest of loud audious are still a little bit loud and some really quiet ones are a bit hard to hear but it works fine.
You can experiment with the threshold value to get something you like, keep it below -40.