I'm a user of M-Audio Delta 66 and I had the same problem on all distros, and i disliked the alsa-tools package because it gives me a few other apps alongside envy24control that i never use, so instead of installing alsa-tools what you really do not need to is go to the terminal and type alsamixer which is installed by default on all linux distros, then press F6 to select the sound card, and bring the DAC0 and DAC1, exit the alsamixer and alsactl store ... problem solved 🙂
I really dislike that PulseAudio which is now used as the default sound system in most distros doesn't have an option to manipulate channels of these type of sound cards ... would love to hear some feedback if anyone ever succeed in doing so without using the alsamixer