Duck sound effects if music is playing

With code, You could set MasterAudio.MasterVolumeLevel to a lower volume during that song, then set it back after. That property will affect the volume of all SFX at once.

So there's no way to do that with Master Audio without writing some code yourself. However Unity 5 will have much more flexible ducking and will allow you to do that natively. I suggest you either download the beta or wait for it to release. We aren't going to add more ducking functionality because of the upcoming Unity features.