Audacity is an audio editor always used for editing brstms in brawl vault
So if you wanna turn up the volume just extract the brstm as a wav,
import it in the program, Audacity and go to effects.
Select amplify and another window will show up asking you how you want the audio loud.
After you edit it in audacity go to brawlbox. Click File>New>Brstm Audio Stream
Then It will ask you to make a loop for the audio, but if you don't want to that's fine
Make sure you have one of the latest brawlbox though, cause when the old ones encodes the audio the quality is not that good.
So yah, this is all I can say