PS: I took a look at the AYP website. It is junk and i wouldn't trust it. When the author is advertised as "Yogani, is an American spiritual scientist" and equates "Tantra == Sex" it is nothing but a marketing scam. Stay away and read the original texts and form your own interpretation.
And of course, how could an American have anything valuable to say on the subject of yoga? /s
Ok champ you obviously know best. Good luck. Jeez...
My post was intended to point people to the authentic sources of Tantra/Hatha/Laya Yoga. If you have a different opinion, that is fine.
Leaving aside the fact that the language of The Serpent power is NOT difficult, two of the three people i have mentioned are Britishers while one is an American. Thus all of their writings are comprehensible to a westerner though the subject matter is complex and takes some time to comprehend.
For authentic sources, start with the book The Serpent Power by Arthur Avalon (real name Sir John Woodroffe). He was a Britisher who was a High Court Judge in Colonial India who was so fascinated with the entire subject matter of "Tantra" that he studied Sanskrit under native Indian scholars and translated a lot of Tantric texts into English. For a nice picture book with rare photographs on the same subject matter, see Kundalini: The arousal of inner energy by Ajit Mookherjee.
The above will give you a solid foundation after which you can move on to other original texts.