Yesterday I extracted every single texture from REZ and the beta, and found a few cool things.
It seems that at some point REZ was going to have a difficulty display on the area select menu
The artist bit interests me too.
N----World was Underworld, their music was implemented in the beta, but was never allowed into the final.
Richard.D.James (Aphex Twin)'s music could not be used, and was not implemented.
Ken Ishii's music was not implemented yet.
The Chemical Brothers are the same as Aphex Twin.
Adam Freeland is the same in the final.
The game uses a system called MainFlow to control when an enemy is spawned, or when an event such as a BPM change occurs, and can be edited with a Dreamcast keyboard in the beta, you can mess up the level by spawning to many of something, like a password protector, and you can make your own scenarios. The only problem is that you cannot save.
I'll post more as I find out more.
EDIT:Here are the textures, everything you need is inside the .rar