How to turn volume down on games that have no volume control?

Hi everyone, the issue I'm having is that the default volume on games is a lot higher than the highest volume of Spotify or iTunes.

Is there some way of manipulating the volumes of the different channels of audio going through the native soundcard so I can have games sound fx at a pleasing level relative to the music?

Thanks

(Oh by the way I'm using 10.4.11)

Use the volume Up/Down keys on the top ,of the keyboard? They won't control different channels though, just the total volume.