Don't you know of a program that amplifies MP3 songs? I have a portable MP3 player, but it plays very quietly. So it occurred to me to amplify the songs. But that quality will go dill, huh?
MP3 is a lossy format (at the very size), so you can say to some extent that you don't know the difference in quality. Personally, I use Audacity to edit the sound, because it's free and so far I've done everything I needed it to do. But I'm not sure if it will be suitable for mass editing of songs. There may also be an automated tool that modifies the selected files based on the specified criteria. Or maybe you could just buy better headphones.