Greetings Jerry and Wu and everyone else,
I think I can guess at the source of your comments about Neo-Confucianism. It brought a smile to my lips. I must confess, however, that when I first read about Zhu Xi, I was quite pleasantly surprised by what he had to say and found his cosmology surprisingly engaging.
Most of what I know about Confucianism I learned through reading De Bary's Sources of Chinese Tradition. This was the first work I had encountered that presented any aspect of Confucianism in a sympathetic light.
I found the section on Neo-Confucianism and Zhu Xi's thought a delightful surprise and a good complement to things I had only encountered in Daoist writings before. Despite having grave reservations about many traditional views espoused by traditional Confucianism, I generally have a positive view of Zhu Xi and share Louis' curiosity about what exactly puts you off in Neo-Confucianism. It seems to me that there were a whole lot of ancient philosophers who espoused stuff that strikes the modern ear as quite "pompous" and "silly" and would not rush to put Zhu Xi in the forefront of this bunch.
I believe I recall reading Waysun Liao's book with profit, but cannot find my copy at the moment to confirm this.
A book that I would recomend to get a quick flavor of a wide variety of Taiji-related philosophy is The Dao of Taijiquan: Way to Rejuvenation by Tsung Hwa Jou
. You can go to that link to amazon.com and read some of the reviews to get a flavor for what the book might have to offer you.
I would caution, however, that survey books that try to approach Taijiquan as a whole, rather than address discreet issues or the teachings of particular masters, tend to share an inevitable weakness. There are many aspects of practice about which practitioners differ. Trying to describe Taijiquan as having consistent positions on all issues forces authors to take personal positions on many questions, often without the opportunity to make readers aware that their positions are by no means universally accepted or may not even be near the "center of gravity" of the greater Taiji community. If you assimulate too many categoric statements of principle early on in your study, this can complicate later practice if you run into teachers with differing positions. It can also complicate your ability to interact with fellow practitioners who may have valuable insights, but espouse ideas you had assumed were not permissible or somehow inherently faulty. If you take what you read with a grain of salt, however, and keep an open mind, you can avoid these potential pitfalls.
As far as the Taoist/Daoist nature of Taijiquan is concerned, there are a few things you may want to note that are alluded to by some previous posts. First, much casual writing on things Chinese does not accurately define what is precisely Daoist in Chinese culture and what is not. Many early Chinese cultural works and concepts were actually adopted by many schools of Chinese thought and are part of a general Chinese cultural heritage. A work like the I Ching/Yi Jing is a good example.
Sun-tzu's/Sunzi's Art of War is another work that probably underlies some of the martial theory in Taijiquan. It has concepts that resonate with many Daoist and Confucian theories, but arguably stands outside of both traditions. Even the term "Tao"/"Dao" is something that is used in both Daoism and Confucianism, with somewhat different meaning and with rather different emphasis in each.
Among intellectuals, many schools of thought were fiercely opposed to each other and persecuted each other where possible. Among ordinary people, a more eclectic attitude was generally the norm than what probably has been usual in the West. In my view, the Taiji classics generally exhibit this eclectic attitude and attempt to appeal to notions that would have been part of everyone's daily cultural heritage, rather than part of any particular sectarian beliefs about Daoism, Confucianism, or even Buddhism. Polaris's post echoes this view in my opinion.
A rough analogy with American realities would be trying to disentangle what is the precise origin of American democratic institutions in "Judeo-Christian values," explicit biblical precedent, pre-Christian Roman governmental institutions, ancient Athenian ideas, pre-Christian German tribal law, and even the Iroquois League. All of these things arguably show up somewhere, but implying sole credit or even predominant credit to anyone of them probably overstates the historical case. In reality, American democracy grew out of the general cultural environment, which had many influences.
The Neo-Confucianism that Polaris also refers to was founded in cosmic theories that have close affinities with Daoist cosmology; as a result, much of what Taijiquan has to say about Yin and Yang and about movement and stillness can be comfortably approached from either perspective. In reality, though, the Taiji theories probably draw on both traditions separately. For example, I would say that most of the ideas about softness and hardness come from the Tao Te Ching/Daodejing, but much of the talk about Wuji and Taiji comes from the Confucian Chou Tun-Yi/Zhou Dunyi. To complicate matters further, Zhou Dunyi's views were apparently later adopted by many Daoists, further muddling what philosophy is truly behind what.
Below is a good link that discusses some of these issues and that delves into some of the philosophy by quoting from original sources. The short essay by Zhou Dunyi in the middle of the link, entitled "Explanation of the Diagram of the Supreme Polarity," should really be required reading for anyone who wants to get serious about Taiji philosophy. This is probably even a principal source of the name of the art itself. I would also recommend a look at some of the footnotes if you want to get a really deep appreciation of some of the philosophical and historical niceties.http://www2.kenyon.edu/Depts/Religion/Fac/Adler/Reln471/CHOU.htm
It is also worthy of note that the Taiji Classics have references to certain Confucian moral imperatives and pithy sayings that almost certainly have nothing to do with Daoism. I think an example is "abandoning self and following the other." Questions of person-to-person ethics have typically been much more a preoccupation in Confucian thought than in Daoist thought. The latter tends to be concerned with relating the individual to his or her environment, nature, and the Dao itself more than to other individuals per se. These things tend to be lesser or non-existent concerns in most Confucian thought, except to the degree that they relate back to person-to-person ethics.
Another thing you may want to know is that asserting that Taijiquan is explicitly a Daoist practice is commonly done in the secondary Taiji literature; however, it is often associated with a widely reported theory about the origin of Taijiquan that is controversial to many and somewhat offensive to parts of the Taiji community. You are welcome to believe and assert what you like, but realize that attributing the creation of Taijiquan exclusively to Daoism and Daoists can be interpreted by some as denying the validity of their teaching lineage or marginalizing the relevance of their practice to the rest of the Taiji community.
I should rush to say that I personally find nothing offensive in your post, even though some of your phrasing begins to tiptoe around potential controversy. In your shoes, however, I would want to be made aware of the potential problem. I should also say that I personally find that most discussion of controversies like the one I refer to fall in the category of things where people tend to speak too quickly and too categorically based on too little real evidence.
The most scholarly-appearing treatments of the origins of Taijiquan tend to raise quite complex and perplexing historical questions, but reserve ultimate judgment about what actually happened and why. I think that most practitioners should similarly reserve judgment about such things and content themselves with following the insights of whomever they perceive to be the fountainhead of their particular teaching lineage, whether such person is ancient or modern. There is no reason to believe that anyone has ever had a monopoly on good ideas and that one shoe has to fit everyone the same. I think that practitioners should make sure to identify the characteristics of the particular shoe they want to wear, but should not begrudge that other people make different choices.
Good luck in your search and with your practice,