@Kelzanelie: depending on exactly what features of CM you rely on, you can get by with some early 5.4.2 version, IIRC (check CM's first post).
(Because, yeah, a downgrade to 5.4.0 is a completely different matter, and I'd recommend having experience with a more indestructible device (Kindle Touch) first

).
(And, yeah, you can't go lower than 5.4.x on a PW2, I completely missed that you were trying to do that, my bad! To avoid confusing other posters, please fix your profile to mention PaperWhite 2 (or PW2)

. [Your first message was completely accurate on that front though, I just completely forgot to make the PW2 + 5.3 == big no-no connection ;/]).