Emptiness schools often critique energetic schools for merely getting caught in other layers of cyclic existence (and worse, creating intense karma in those layers). Yet emptiness schools often don't admit the valid energetic part of the path.

The first yoga of the six, the crux and foundation of this 6-yoga system, explains steps that produce bliss - and resolve it into emptiness. This resolution occurs within the mysterious deep-centers, who reside along - and whose vitality is integrated through - the central channel.

The Seventh Dalai Lama wrote verse about the 6 yoga system, whose 1st paragraph follows. Much of it is of specific cultural reference, but the 4th and 7th lines speak to general theory:
"Namo guru daka dakini yeh!
O all-pervading Heruka and your mandala of bliss,
O Tilopa, also known as the sublimely wise Jnanabhadra
Who took the insight of ecstasy and void to its limits,
And Naropa, an emodiment of Chakrasamvara:
I request you, bestow blessings, that we may achive
The wisdom of ecstasy and void conjoined."
- (from page 96 of the book)

In it, he traces the history of yogic philosophy and its development over time, emphasizing its role in spiritual unfolding. He does not include any yoga postures, leaving that up to individual instructors. "Yoga is neither a religion by itself nor part of any other religious system," he says, adding that "yoga is universal and a yogi is not necessarily bound to any particular religious faith." He defines it as "the union between the individual self and the universal self." Yoga is available to anyone who wishes to accept its discipline.

Muni discusses yoga practices relating to a variety of areas, such as rebirth, karma, the purpose of life, bliss, human consciousness, and suffering. Although yoga is an ancient practice, its underlying philosophy is timeless and still relevant to those wishing to transform their lives. Classical yoga focuses on spiritual development and the attainment of higher levels of consciousness, and this is what Muni concentrates on throughout his writing.