How do I make the main mix of my song louder?

This is not a hardware problem, nor is it a driver problem.
 
If the final mix wave file is quiet, then it simply needs to go through a Mastering stage.  Proper mastering is no easy task (that's why there are mastering engineers), but you can do very basic steps (like increasing volume) with Sonar. You can either import the final mix, or simply apply some plugins to the MASTER OUT on the song itself.
 
What you want to do is apply a brickwall limiter to the final mix - but you don't want to over use it. Your Sonar (VS or Full) should come with Sonitus FX. Add the Compressor, and choose one of the mastering presets. That is just a basic starting point, but you will immediately notice an increase in volume.
 
Do a google search for Mastering, Loudness, Loudness Wars, limiting, etc...   There is a lot of info out there regarding all of this and there is no single "right" answer.

Try any of the fine copressers that come with Sonar/Sonar VS.  It is trial and error.  A compressor will limit the loudness while at the same time raising the floor.  I have worked with external gear since 1980 and with digital since 2000.  Record your presets to recall them at a later time.