At Arcane Haunted Houses, we think it's perhaps the single most important element. We always have a PA with a main soundtrack, compiled from various sources. That part we choose to keep secret. What we will say is not so cryptic. Quiet, creepy noises where you least expect them tend to be more unsettling than beating folks over the head with slasher film music.
Diversity is key.
We do use computers for some of our soundtracks. But for right now, we go with what works.