The main text is from http://www.shivashakti.com/mat2.htm . The comments in brackets are mine.
Chakras and the 64 Yoginis
As the first of the siddhas, the Tibetan sources mention Luhi-pa (Luyi-pada) who is most probably identical with Matsyendranatha, the teacher of the famous Gorakshanatha...The natha-siddhas...deserve to be singled out for separate treatment by virtue of their enormous influence on the development of Yoga - Textbook of Yoga, Georg Feuerstein,ch 10
There are more systems of chakras in the tantrik tradition than most people realise. One of the most ancient appears in chapter nine of the Kaulajnana Nirnaya, attributed to Siddha Matsyendranath. Said to be the progenitor of the Kaula school of tantra, this chakra system is eightfold. Each of the lotuses has eight petals and these represent the 64 yoginis, famed in Kamarupa [form, body or character of desire] .
"The letter kSha is in the Brahmarandhra [anterior fontanelle] , la in the forehead, ha between the eyes, sa in the mouth [at the back above the soft pallet] , Sha [retroflex sha] in the throat, sha in the heart, va in the navel [most likely this is the solar plexus] , and ha in the genitals [the whole pelvic region to the true navel] . Dear One, listen to the collective meditation in these chakra places.
"The first of the eight is a celestial eight petal lotus of pure crystal effulgence, a heavenly fire or flame, completely without stain, free from all duality, from the fires of cruelty, devoid even of nothingness. One should avoid perturbation and practise equipoise (Sama) consciousness. One my see even beyond the future, one with the endless circle of time, having knowledge of what is spoken at a distance, able to both grant boons and to paralyse, with the ability to seize and subjugate pashus [normal people] , or to destroy or to kill them, mortal, always truthful, and in equipoise, becoming eloquent, a Siddha, and able to do anything.
"One should meditate on the second as having eight petals, as bright as a beautiful pure flame. One conquers death and becomes the cause of great excitation. Meditating one-pointedly on this multi-fold form one becomes an emperor amongst kings, doing whatsoever one wills, and may destroy all in the three worlds, whether animate or inanimate - like Kruddha, the cause of both creation and dissolution, always engaged in love.
"The third great chakra is the deliverer from the nine tattvas. After meditating on the Guru in that chakra for six months, one my achieve whatever is wished for, destroy old age, be able to see at a distance, able to obstruct, even if one hundred yojanas distant. In a lonely place one should meditate on that multi-fold form.
"The fourth chakra is the cause of peace, increasing happiness and pleasure. By always meditating on it, afterwards one becomes immortal, eloquent, victorious over death and disease. Practising it daily, one causes death to flee. By continual practice for a period of sixteen seasons on this great chakra, one becomes able to destroy in a day and a night.
"O Surasundari, the fifth great lotus has eight petals. One should always meditate on it as being of a smoky colour, then one my shake the three worlds. It causes eloquence and avoidance of untimely death, and allows one to both enslave and paralyse.
"If one should meditate devotedly on the sixth royal chakra, fiery, with a pericarp of eight petals, as bright as liquid gold, the cause of Iccha Siddhi, it enables one to see into the future, giving Anima and the other seven siddhis - of this there is no doubt.
"Dear Mahadevi, the seventh is as bright as the full moon, auspicious, within the body, bestowing both enjoyment and liberation, destroying fever and death, enabling one to enter into another's body. what may not be done? One becomes the best within a circle of people. "Pretty-Eyed One, the eighth great chakra, adorned with eight petals, gives Dharma, Artha, Kama and Moksha."
[Notice the order is descending. That, however, may be a quirk of the text to be "corrected" by a guru. Notice the abilities progress from lower cakras to higher ones. I've been practicing this and it is both potent and simpler than the version that corresponds letters of the sanskrit alphabet with the various cakra petals. One of the reasons that versions is not so balanced for westerners is because the petal tones aren't emphasized. People tend to stick with the center seed syllable of a cakra, the laM, vaM, raM etc, and don't consider the petals except through visualization.
Tantric texts usually don't emphasize which letter goes to which petal, however. The sanskrit alphabet is to be mastered as a kind of rosary going up the spine around the central path. In Matsyendranath's version the petals are visualized, and sometimes yoginis are associated with each, but the eighfold petal arrangement carries the central tone and no additional ones are really needed. You can start this as a descending path as the text describes, but the real work goes on the ascending path, with the descending path being purifying and preparatory. When you intone each seed syllable the traditional nasal final follows, either a brief emphasized M that vibrates the nasal cavity into the head or an Ng that Tibetans and north Indian traditions use. The former is gentler and more feminine, vibrating the aura more and the latter is more defined and vibrates the spinal column more. Contrary to mantras like OM the final nasal is usually a sound more brief than the letters preceding it. It's like a quick tap that you allow to reverberate silently after you briefly touch it.
The sounds are also not quite explained. The compound letter kSha is similar to the Greek ksi and the latin x. The difference is that the Sh is retroflex (with the tip of the tongue at the roof of the palate. A more accurate sound is the Sh being more a Cha (like the English loch) sound at the back of the throat. The sanskrit la is really in between a latin la and a tha (as in that) where the tongue doesn't quite touch the teeth. You'll notice ha is repeated, associated both with the genital and brow areas. The sound actually varies slightly between the two. The lower ha is the traditional one, described as a gutteral voiced aspirant, meaning you do not breath out silently but voice it from the back of your throat, as if trying to pronounce a continuous hard g (as in goat) with the breath. The upper ha is just a tad more silent. The thing to know here is that the sounds by themselves do not vibrate the cakras. It is when awareness is placed in those areas and the sense of 8 radiating extensions is felt and/or visualized that the sound actually does the work. Then you can subtly play with the sound to fine tune the sensations.
The siddhis or accomplishments are of the subtle bodies, especially in the higher cakras. Abilities such as changing shape and size, moving into another body (something Matsyendranath was said to do on occasion, once getting caught up in the body of a raja because of the latters harem being so demanding). On the other hand the nature of reality is different to one in those states so event and form change are from that perspective. Notice also the time advised to focus on each cakra (only mentioned for a few). This isn't something to be done in a short period, that's for sure.]