Is New Age music a front for Satanism? It sounds pretty funny when you say it straight out like that, as most people who listen to New Age music probably don't take the concept of Satan all that seriously in the first place. But the idea is actually pretty widespread among a certain type of Christians, some of whom do indeed see New Age music as an insidious plot by the Lord of Darkness and his earthly minions.
To understand this bit of lunacy you have to first understand two others. The first is that this type of Christianity- not all or even most Christianity, just this type- is a closed worldview. My father's best friend for many years was a Christian minister, and he knew my father wasn't a Christian, but they were still best friends. By contrast, the people who think this way generally go out of their way to avoid interacting with anyone who doesn't already agree with them. The news programs they watch, the books they read, the music they listen to and the company they keep- all of these things are tightly controlled to prevent them from receiving any outside information. I personally think homeschooling can be a wonderful thing, but the reason people like this do it is so their kids will never be exposed to any outside ideas.
The natural effect of all this is that things that would seem crazy and outlandish to the far majority of people seem normal and reasonable to this type of Christian, because they simply don't have the context to understand them.
The other thing about people like this is that they almost never have a sense of humor. They take everything absolutely literally, from the Bible to Ozzy Osbourne. So when a particular New Age album is described as “helping you find your spirit guide,” it never even occurs to them that you might mean something different by that than what they would mean. Having insulated themselves from other worldviews, they have no more than a vague notion that other worldviews even exist. So when they see the word “spirit,” they can only interpret that to mean a demonic entity, a soldier of the Legions of Hell, and they take that concept 100% seriously.
From this warped perspective, the notion that New Age music involves the literal invocation of demonic entities is not a laughable bit of hysteria as most people would see it, but a sinister and terrifying reality. That's the mindset of the True Believer.