If you're using Unity, you can actually add the sounds to an empty game object and manipulate the audio through a slider until the balance feels right. What I did was just lower/raise the volume on the sound I wanted to play and then had a AudioManager script that was called from other functions and told to play a specific audio.
Once that happened, I just manually lowered/raised the audio until it felt nice during playtesting. I don't know if that's the fix you were looking for, but it did work. : )