When people discuss about the Tao they invariably make references to the Tao Te Ching and the Zhuangzi. Nothing wrong with that since Laozi knew much about Tao while Zhuangzi told stories and anecdotes about the ancients, and of the cultivation of essence (meditation). However, it does not mean that their ancients, Fu Xi, Shen Nong, and Huang Di did not know more about Tao than them. Unfortunately, these ancients left no traceable records of their existence or profound knowledge over the long passage of time (> 3,000 BC). Until the records are found or discovered, the so called modern scholars will not be convinced of their existence.
The earliest historical record extant in China is that of the Book of History (Shujing) said to be compiled by Confucius. It recorded the rules of Yao, Shun and the Great Yu, followed by the three dynasties of Xia, Shang and Zhou. Confucius had also made references, in the Analects, to the Book of Changes (Yijing/ I Ching) of these three dynasties. The received text of the Book of Changes made available to everyone nowadays is that of the Zhou often referred to as the Zhouyi for short.
The wise King Wen was accredited to have written the judgments while his son Zhou Gong was accredited to have written the lines to the sixty four hexagrams of the Zhouyi. Their wise advisor and war strategist, Jiang Taigong was accredited to have written the Daoist text, Yin Fu Ching.
Both Laozi and Confucius who lived 500 years later had studied the wisdoms contained in the Zhouyi and extolled the virtues of their ancients. Each went on to leave behind to posterity their lucid understanding of ancient thoughts and of the Zhouyi. While Confucius followed the thoughts and practice of Yao and Shun, King Wen and Zhou Gong; Laozi probably followed the thoughts and practice of Fu Xi, Huang Di and that of Jiang Taigong.
The dual cultivation of essence (Tao) and of virtues (Te) for the attainment of Tao is contained in the Yi for the right person – the Junzi.
If Daoist scholars and Yi experts earnestly examine the Tao Te Ching and the comments of Confucius in the ten wings, they could find out how the Daoist and Confucian doctrines linked up with the Zhouyi. Obviously without a deep understanding of the cultivation of essence and bodily life, and the requisite knowledge of the Yi, their task would be doubly hard. They may also have to know a bit of Chinese to translate the TTC and some words in the Yi. (The scholars and/or the cultivators who translated the TTC into English seem to get it but sometimes not, therefore one cannot recommend any.)
A good start, since both Laozi and Confucius often refer to Heaven and Earth in their teachings, is to thoroughly understand the two primary hexagrams, Qian Kun (representing Heaven and Earth), in the Zhouyi. It is not for nothing that sages and the wise down the ages often point to these two hexagrams, since Qian Kun relates to Tao. (Also refer to the Great Treatise and Daoist texts)
The holy sages long before the time of Laozi and Confucius had incorporated the study and the cultivation of Tao within the Zhouyi for the right person. Laozi was the first followed by others who recorded their understanding of the underlying thoughts on Tao contained therein to those who came later. (Think Zhen Ren and Daoist heavenly immortals)
Perhaps you can be a right person too if you truly understand the workings of Heaven and Earth or Qian Kun. If you want to understand where Confucius got some of his ideas study the eight trigrams thoroughly.
There is a Chinese saying that if a student can understand an ancient classic (Jing / Ching), the person can understand all classics. Perhaps it is true. How would I know? Since many of the things said in this entry go against the very grain of the attached thoughts and beliefs of the so called modern Daoist and Yi scholars.
Please find out for yourself, if you are really keen but do not forget to use the Richard Wilhelm translation of the Zhouyi for the research otherwise you could be at a loss as to what the ancients actually said. If you can find the links between the TTC and Confucius’s thoughts with the Zhouyi, well and good. However, if you fail to, you could still achieve more clarity than other students or perhaps even the modern scholars.