Program to balance speaker output for surround sound 2.1?
Install Pulse Audio Volume Controller (aka pavucontrol).
Open up your Terminal and execute these commands:
sudo apt-get install pavucontrol # Install
pavucontrol # Run
If you are doing it by ear, I would simply download a wide-band pink noise (which is random noise, equal energy per octave - which is the balanced sound you are after) sound file and play it back and set the levels between your speakers until they sound even.
The following link has a series of different test tones and instructions on how to use them: http://www.eminent-tech.com/music/multimediatest.html