I have been using the free Audacity program to normalize, edit and amplify my music, and it is a great little program.

Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems. You can learn more and download Audacity here

This open-source program includes audio recording tools and sophisticated editing functions. You can even create audio soundscapes from scratch. You can add any of several dozen effects, use a sound mixer...in short, the app has everything you might need. While you don't have to be well-versed in sound editing to use it, people with some experience will particularly enjoy its power. 

One of the things it does is allow me to amplify and normalize my music to enhance my Sansa listening.

I will be doing a complete video walkthrough of the program soon but in the mean time this should get you started.

Click the image above to begin the step-by step tutorial

After you've completed your Amplification, play through the song, and make sure it meets your expectations. Amplify will edit the entire song unless you select a section specifically.

Once you're happy with the changes, simply click Save (NOTE: This will save over the original song unless you Save As something different).

Let me know if you have any problems or questins on this. We would be glad to help.