G8 theory

Of course if you have a good understanding of Grade 5 theroy, it's helpful in your Grade 8 theory. However, grade 8 theory covers a more wider range of musical aspects like harmony, counterpoint, music composition, modilation, brief music history, orchestration and music analysis. If you study only ONE book about music theroy(AB guide to music theory part II), that not quite enough.
Just find a good teacher to guide you on the Grade 8 theroy. The exercises need quite a lot of practice before you can get a pass.

所有音樂理論都是相關的, 不可能是一個獨立個體
5級theory只是一個基礎, 一定要熟習
否則學8級theory會有一定的難度