I've finally released the packMP3 source code for everyone to optimize and toy around with it. It is attached here and you can also download it from:
www.matthiasstirner.com.
packMP3 is a compression program specially designed for further compression of MPEG-1 Audio Layer III audio files without causing any further loss. Typically it reduces the file size of a MP3 file by 16% based on tests with 6000 randomly selected files.