Exactly the same thing happened to me couple of days ago, I heard the same "cacophony of voices, like dozens of different voices and sounds all blended together" like you said. I also noticed that I was in sleep paralysis at the same time, however I was too stupid to recognize this was the transition to a dream so I panicked and quickly got out of the whole situation and woke up. Sucks, because this actually happened after WBTB.

You say you had this WILD-experience at the beginning of the night, I envy you, I can only do it after 1 hour WBTB and even then it's very hard to fall asleep again.