What's this music in "World of Ice"?
I finally managed to dig up the track that I wanted after I listened to a number of Penguindrum-related uploads on SoundCloud; it was listed as "Karei. Sora No Ana Bunshitsu". From some more searching, it appears that this can be found on the bonus CD of vol. 3 of the Blu-Ray. This all indicates that this was probably an original composition.

I'm unfortunately still having trouble figuring out what the original Japanese name of this track is; English websites so-far have only given romaji transcriptions of the title, and searches for "そらのあなぶんしつ" thus far have not yielded any particularly promising results. (It does not help that I don't really know Japanese.)