oke so lets think a bit about it, why akasha and alche didnt got the book? hmm its somehow mystery, all i know is that cube/book protects its self, but also lets think a bit again about it, why cube, whats inside it? well inside it is what you put into it, if we look at cube which angien "pulled out of ground and smashed it to release/create our realm" then other cube golemus brothers used to create golem, but cube went unstable and golemus golemicarum was result, so in both cases cubes lost their shape/stability and created new world or new part of it, so in order to do something like that, i mean to create realm/world/universe, what ever, so principals are rules on which world is based on, so lets imagine universe, well to make it simple imagine a cube and put in it all principals ya want, it could be 1,2,3,5,10,20, etc principals, its up to you to think of how many you can imagine and put into one pile, so this principals are rules, so you assigned this rules to your imagined world, and this world will continue to grow/evolve/expand/(wot ever), by this rules (principals), so to cut other staff out i will just say that my point is that cube COULD be itself book of principals coz in it are principals, well it could be that its real book in cube, i mean book with explanations, written by hand, but it could be my first guess that it is called "book" becoz of metaphorical meaning
also dont get me wrong i dont think in cube is other world, i just think in it are principals and nothing else, principals wont shape anything if in it is just space/nothing, and principals are balanced inside it, so nothing can work out, first cube i mentioned in here built this realm only after angien "released" it, so principals got in touch with energy/matter and world got created, in second example cube it self was created by base elements but there was only 3 of them, so without 4th element there was no balance and cube got unstable
just some thoughts