I FOUND CARL LOEWE'S VERSION OF "DER ERLKOENIG" ON YOUTUBE. :D :D Two versions, in fact. There's this one, which has better sound quality:
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And then there's this version, which I prefer because I think the singer does a better job of differentiating between the characters of the Father, the Son, and the Erlking:
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Regardless, this makes me a very happy music nerd. :3