I can't get GarageBand to export the audio edited files successfully

I did what the previous writer suggested and made sure my preferences said "export at full volume". I raised the volume level to the MAX on both the chapter track and the master track. I checked the inputs and outputs on my Mac. STILL NO LUCK. What I'm finding is that the original file at a low volume and the new updated file with increased volume both sound EXACTLY the SAME once I've exported them to iTunes. Why is this? I've spoken to several support people at Apple. Nobody seems to have any ideas.