Questions about the sound spot in the module files.

Well, i noticed some sounds appears too weak in the game even if i amplify em and make more clear, and even if i put the sound volume parameter to 100 (for example).

1.- How does the “soundvolume” parameter of the module files work? in fact, it works already? wat is the maximum sound level we can write there? (2?, 10?, 100?).
2.- Is there something like a “sound_prirority” parameter that should tell the module to sound before any one else??
3.- Wats the difference between using ogg, mp3 and wav files???

Thx in advance.