Zhan Zhuang, as a terminology, is not a secret but its methodologies are "secrets" if not mysterious. Basically, those MASTERS who earned lineages have their art's most important informations....and that is not something one can ask for. As you know, it is the Sigung to Sifu to Student that builds a lifetime of experiences, trust and earning the lineage.
As an Asian myself, I know that though we open up to the WESTERN world, there are things retained...sometimes they are coded within Poems and songs. I don't believe the wholeness was already laid out for you, for a lot (not all) masters would retain at least 10% of their knowledge to themselves to protect themselves...it may sound selfish but it is.
Here are some basic though on Zhan Zhuang and Yi meditations:
Zhan Zhuang, though a Yin meditation, is also very much a YANG practice of strenghtening the lower basin as they call it. the MA BU stance or the horse stance. But the internal part is the absorption of CHI from environments. It is also the dissolving of blockages and the opening of meridians...lastly and the most important of all, is the direct absorption process of CHI being hardwired to our DAN TIAN than can be accomplished only if our minds are in the beta mode. A Yang mind cannot "see" or feel the Yin mode.
This Zhan Zhuang practice is really a Yin method of cultivation though packing of the YANG energy on the Dan Tian. Every major internal arts have distinct NEI KUNG practice that is unique and therefore different flavors by themselves. Pa Kua, the circular, Tai Chi, the yielding and Hsing-I the most YANG of all the internal arts.
Please read some of these books that would give you "hints":
1. MAGUS OF JAVA by Kosta Danaos...www.wenwu.net
his master is John Chang, a hsien who can levitate, do pyrogenesis (create fire from nothing), Telekinesis (moving objects and opponents), and much more. John Chang is a Chinese master of Pa Lei Chuan, 8 ways thunder boxing, a direct lineage from Mo-Tzu and Bodidharma.......http://www.wenwu.org
2. EMPTY FORCE by Paul Dong, Chi Kung master, researcher who documents the phenomena of CHi acquired thru Chi Kung and Nei Kung....worked with top chi kung, nei kung masters....good material
3. Warriors of Stillness, by Dan Diepersloot, a student of Master Cai who can move and blast opponents with his CHI with or without physical touch. Very good and informative history and evolution of TAI CHI and its "secrets"....He is a Nei Kung Master who only knows only the "BASIC" of all TAI CHI, the GRASPING THE BIRDS TAIL but stresses the forgotten practice of STILLNESS meditation as a prerequisite of all internal arts.....The website below is also the most famous proponent of the STANDING STILL MEDITATION.....http://www.yiquan.com.pl/training.html
With these info, one can see at least a better distinction between CHI KUNG and NEI KUNG though the practice is an overlapping and almost identical one. The most obvious difference is that in most CHI KUNG, bearing the name CHI, which in this case, the literal AIR or VAPOR, PNEUMA in greek and PRANA in Indian...is Breath dependent. The Breathing techniques that leads the CHI...while NEIKUNG is totally dependent from the YI-I or intention, will or desire.....the overlapping is indistinguishible and impossible to isolate from both practice.
And so, YANG TAI CHI, despite the YANG family's generosity, remains intact within their own clan, a practice that can only be learned if earning their own lineage.
The mysteries of the CHI and TAO is infinite and the practice of TAI CHI is only scratching the surface. Some believe that we all rely totally on our KARMA whether the DOJO (will of heaven) will favor us in learning all truths.
Chan Sang Feng, Sidharta Buddha, and Bodhidharma, according to master John Chang, a Chinese Hsien living in JAVA...claimed that only 3 people known to have given the grace of the TAO to see all.
PEACE and good luck on your practices,