What is the significance of the recording played during the coffin scene?

According to IMDB http://www.imdb.com/title/tt0251736/trivia?item=tr0766954 it is one line from Aleister Crowley's poem "The Poet" (as recorded by Crowley himself) repeated over and over (and also slowed down). The line is "Bury me in a nameless grave"

In Captain Spaulding's establishment, there are reproductions of some of Crowley's paintings as well.

As for the significance, it's hard to say. Crowley had a strange sense of humor (for example, he referred to masturbation as "human sacrifice") and many of his writings can be taken in a variety of ways. He is often linked with satanism, though I believe that had more do with the fact that he was an anti-christian, occultist drug addict that was openly promiscuous and called himself "the Beast," all in the early 1900s. My guess is that Rob Zombie just thought it sounded creepy as hell and it worked in the scene.