Where is the central channel connecting the chakras?

Where is the Central Channel (central Nadi, 中脉) connecting the chakras (wheels)? According to the tradition of Tibetan Buddhism, some classic texts say it is inside the spinal cord and some say it is along the center of the torso (i.e. hanging in mid-air centrally). Which is more correct?

Before we tackle this question of difference in opinions, perhaps we should look at another question: why do we have to pay attention to the Central Channel in our practice?

The ultimate objective of Tibetan Buddhism is to direct (Kundalini) energy generated at the lower chakras up towards the head chakras to attain the Enlightenment objective of experiencing our true self: Emptiness (空。or 缘起性空 [an Enlightened one views everything from Emptiness]).

Similarly, the ultimate objective of Taoist meditation (Neidan) is to direct energy to the mysterious aperture "discovered" between the inner part between one's eyebrows, for purification into the original state of pure Yang (纯阳) or Tao.

Psychologically speaking, the process aims at raising oneself above one's limiting Self, to a higher level of perception devoid from all worldly connections. And only from this perspective, according to this line-of-thought in spirituality, one can be free from the limiting (and passive, or being conditioned) reactions (both physical and psychological) towards stimuli from the environment (again, both physical and psychological).

As such, the final process leading up to enlightenment can only come through a step without any connection to the physical world. The final step must necessarily be through a path with is NOT physically connected, and which can only be felt (i.e it only exists experientially) during deep meditation. Since the spinal cord is part of the physical world (and can be felt as such by a practitioner), it cannot be the final step. The only channel that goes well with this spiritual belief is the channel located centrally.

The obvious question is: Why are there many classic texts advocate going through the Spinal cord? (note: I'm not talking about the microcosmic circulation here, which is only a foundation practice before anything spiritual can even begin)

In the classic Taoist Neidan text "Taoist Yoga" (性命法诀明指） by Zhao BiChen （趙避塵）, translated into English by Charles Luk), Zhao spoke of Passing the Major Gate (过大关) after a practitioner has successfully built the Foundation through doing 100 days of microcosmic circulation. Passing the Major Gate, according to Zhao, is through meditation without Mindful Push (意). Under this constraint, chi can only go up when it is very strong. This is a preparatory step towards doing it centrally!

Whereas not all Masters advocated having this preparatory step, but skipping this step must be done with utmost care. It is because the path to spirituality is loaded with many dangers (not the least including the danger of self-induced psychosis). If one goes through the literature, one can read accounts of highly seasoned practitioners (in particular self-learners, which probably covering the majority of practitioners in the past decades or so) wrote their accounts of doing chi going up centrally with initially damaging physical or psychological effects!

But then why these seasoned self-learners risk doing it centrally? The usual reason that I can decipher from their own accounts is that they shared the view that "Life is too short for doing it the long way"! Right or wrong is the personal decisions of these highly-seasoned practitioners. Fortunately for most of us, the highest goal of spirituality is an honorable goal that we aspire to, rather than one that we would risk everything to attain. Probably there is the reason why there are not many sages (or prophets/Immortals/Saints/Buddhas..) walking among us!

Central Channel (Nadi) - 中脉