You can adjust sound volume in Flash istelf using a small bit of actionscripting, no need for downloading extra programs:
[SoundName] = new Sound (this)
[SoundName].attachSound("[SoundLinkageName]");
[SoundName].start(0,1);
[SoundName].setVolume(100);
_root.[SoundName].stop();
the first three lines is what you put in the keyframe where you want the sound to begin playing from, and the very last line is what you put in the keyframe to make the sound stop playing [you should only need that when you want to stop a looping sound from playing]
in the line [SoundName].start(0,1); the 'o' means how many seconds you want the sound to start playing in fom [so if it was 2 the sound would play exactly 2 seconds into thesound file]
the '1' means how many times you want it to loop, so for your voices just keep it at one, but for music have it at somehting like 99 then use the _root. line to stop the music
simply remove the brackets and replace what's in the brackets with the right names and paste into your movie, for the AS Linkage names simply right click the sound in the library, then select 'Linkage', check the box and then name it somehting, the name you give it in that window becomes the '[linkagename]' part.
as for the volume, set that 100 value to something higher to make your voice play louder, try 150 or even 200
that concludes my crash-crouse on AS for sound :3 feel free to ask questions