The theory of "Six Books" in Shuo Wen Jie Zi refers to things, pictographs, sounds, meanings, notes and excuses. It is the first dictionary to explain classics in the history of China, and it is a collection of Chinese characters before the Han Dynasty. I think it is radical spelling. Four famous scholars who studied Shuo Wen Jie Zi in Qing Dynasty: Duan Yucai's Notes on Shuo Wen Jie Zi, Zhu's Notes on Shuo Wen Tong Xun, Gui Fu's Notes on Shuo Wen Jie Zi, and ieee fellow's Examples of Shuo Wen Jie Zi. It should be helpful to learn Shuo Wen Jie Zi, which is the most authoritative.
In terms of phonology, the earliest and most complete rhyming book in existence is Guang Yun written by Chen Pengnian in Song Dynasty, which records the phonology between Wei, Jin, Tang and Song Dynasties and studies the medieval phonology.
The earliest record is Li Deng's Music Category.
In Qing Dynasty, Zhang Yushu's "Pei Yun Wen Fu" mainly focused on poetic rhyme and exegesis, which was used to look up the source of words and allusions.
Shuowen Jiezi is a classic. I admire you very much. Let's go