Hello,
Please let me comment briefly on a couple of small points in this discussion:
I think it's important to preserve in English the same distinction that exists in Chinese. "Earth" (di 地) is used to mean the counterpart of Heaven, as in "Heaven and Earth". "Soil" (tu 土) is used to mean one of the wuxing (five agents, phases, elements... whatever you call them). Just like di and tu are related in Chinese (in meaning, and also in the shape of the characters), but are not exactly the same thing, the same is true of Earth and Soil.
I think Wang Mu says that "Soil ... is the Golden Elixir" because, just like the Elixir, it contains and unifies Yin and Yang (the celestial stems ji and wu, respectively) as well as the other four agents (Wood, Fire, Metal, Water), of which it is the origin. Soil represents, at the level of the five agents (the world as we know it), the unity of the One Breath, and the One Breath is the Elixir.
Concerning Wang Mu's "Foundations":
I agree that the book is not exactly easy. Wang Mu didn't intend to simplify Neidan, just to present it in a way as clear as possible. This is the best combination of a fairly extended but at the same clear description of Neidan that I know of among those written by a contemporary Chinese author (and master). It describes all main aspects of the main codification of the Neidan practice (preliminary + three stages) and I also like because it quotes Chinese texts continuously.
I wasn't sure whether I should add a bibliography, but then decided I wouldn't, fearing that it would make the book seem too "technical". But maybe I'll make a short list of works quoted and post it somewhere.
Just one more thing...:
Really this seems to be one of the main points to understand the perspectives of Neidan. Liu Yiming's passage is the most detailed explanation of it that I have read. He also mentions it in other works. But please note that at the end he says:
"Superior virtue and inferior virtue are different and are not the same. Therefore their uses are dissimilar. . . . However, they lead to the same goal."
I don't think "inferior virtue" means someone who is "of inferior virtue". As it does in the Daode jing (and in the Cantong qi), it refers to the way of "doing" as distinguished from the way of "non-doing" (superior virtue).
Thanks,
Fabrizio