Rather than walk through the process I took in figuring this out, I'm just going to lay out the result.
There are three kinds of worlds in SsA: the Kaleidoscope, the Dream Realms, and the Worlds Beyond.
The Kaleidoscope is all the alternate versions of the Great Basin. The vast majority have nonhuman residents, with an Aum that matches them. Most of the Kaleidoscope would be considered "distant parallels" of the Basin.
In a Dream Realm, everything is basically a shared hallucination that you happen to be physically part of. There is nothing in a Dream Realm but what its inhabitants bring in. The GM has my personal go-ahead to plaster Dream Realms with signs that say "I ain't gotta explain shit" because all of it is allegory, none of it needs to be consistent, the life forms there are only aspects of your mental processes, and the only real things there are thoughts and feelings that you bring in with you. A Dream Realm with no thinking beings inside it might cease to exist.
The Worlds Beyond are different. They're fundamentally the "same sort of thing" as the Dream Realms, but they're generated by the thoughts and feelings of Aum - they persist even if there's no one from the Kaleidoscope there.
- Arriving: You can reach the Worlds Beyond via Travel. Each of the Worlds Beyond has one and only one place that connects to the Travel Lattice. Sometimes there might seem to be multiple gateways to different "realms" in one world, but those are actually multiple worlds that someone stitched together so that they (and perhaps the souls of the departed) could walk between them.
- Aum's Mind: Each of the Worlds Beyond expresses a process or complex within Aum's mind. In many ways, the Worlds Beyond are Aum's mind, too vast to be contained by its body. Most of Aum's mental processes seem to map well to the human mind. Some don't. Sometimes you can easily tell what the concept is, as with the literally fiery passion of the Brass Inferno or the paranoid Net of Response. Other times it's not as clear.
- Many Worlds Beyond encourage the human mind to translate local idioms into their own understanding, such as seeing all thinking beings in that place as essentially human-looking. The Sixth Sense reveals the truth. Visitors from other parts of the Kaleidoscope see each world through their own culturally-appropriate visions.
- Aum is not perfect, psychologically speaking. Aum may not even be well. As much as Aum has self-love, there are heavens. As much as Aum has self-hating thoughts, there are hells.
- The Gods: Each of the Worlds Beyond are each centered around one or more supernaturally powerful beings. These gods create the other inhabitants of that world. The gods are always strongly linked to the thoughts of the realm. They have no choice but to express them in one way or another.
- Their Creations: The creatures made by the gods are hybridized with other ideas. Whether you want to call that "less pure" or "more human", they're not just single-thought-forms. Their societies play out certain structures-of-mind within Aum, but they have agency, something the gods themselves have little of. The natives of the Worlds Beyond can change.
- The relationship between the gods and creatures of the Worlds Beyond are the cruxes of those worlds. Some gods bring creatures into being to worship them, or to seek their favor. Others generate creatures to build endless structures, or to explore and report back. Their interactions with souls from the Kaleidoscope says volumes about the state of mind of the local god.
- Afterlives: The Worlds Beyond are also afterlives. If the Uncountable Spinners of Silver Cord did not exist, then souls from the Basin would go immediately to the Worlds Beyond, and eventually leave them to reincarnate, free from the memories of their past lives and their post-death experiences. The Spinners, broken as they are, change this. Some souls reincarnate immediately. Some stay in the Basin for much longer than others. Some remember pieces of their pasts.
- Which afterlife you arrive in is not reliably predictable. Most people go to afterlives their people knew from times long past. Many people are judged by the standards of their cultures. But not always. The process is broken.
