I formulated an operational definition of music long ago.
Music is a nonverbal form of human interaction communicating mood, emotion, demeanor, decorum, etc. through the pleasing and logical arrangement of certain sounds. Being a form of human communication, music is thought.
It doesn't matter what instrument is used, whether it's the human voice or some machine being operated by a human (and horns and harps are machines--things without life, giving sound, as Paul referred to them) there is no music in our world without a human source, be it corrupt or whole.
But I suspect that what SMA means by "Demonic Music" is something that he thinks carries the power of the Devil, and he's probably thinking of the kind of music made by artists like Iron Maiden (I know, that dates me) and Marilyn Manson. I could be wrong. He never comes right out and says what he means.
I don't think any music carries any spiritual power, whether it be demonic or angelic. That's just pagan superstition. It's power is in the carnal realm, and it does affect our moods. We like it a lot, like food and love.
All music has a character quality. Hymns are solemn. Psalms (as a style) are triumphant, joyful. But there were also forms in Paul's day called dithyrambs, which leaned toward the drunken and wild spectrum of style, and accompanied bacchanalian festivals.
There is devilish music, as much as there are other forms of devilish and sensual behavior, like that mentioned above. But music that is truly demonic would possess the very noise of Hell, and couldn't rightly be called music, like demoniacs can't rightly be called men; they're beasts. It would be fearful and disturbing and repulsive even to those who worship devils.