Two ways to increase volume in Sins. The first is to increase the track's volume. I don't use Audacity personally but it should still be straight forward. Be sure to avoid clipping the peaks and causing distortion.
The second way is to go into SoundEffects.sounddata file and play with the settings.
Theshold is the maximum distance the sound will play at.
MinAttenuationDist is the game distance from the camera when the sound starts to fade out, until it reaches Threshold and you cannot hear it anymore. By raising these numbers you can make the sound more dominant and from a longer range.