Jikan wrote:who says that sex-practice is necessary to awakening?
if you want to awaken while alive.
From what I have learned from the works of Tsongkhapa and his followers is that you do not attain awakening through sex but through samadhi
. There are different kinds of samadhi that are described in the Sutras and Tantras. There are samadhis that use sex in some way or another, but here according to Tsongkhapa sex can be part of one's samadhi 1. through visualisation, 2.through the use of non-human consorts, such as Devis etc., or
3. as a human partner,( and here follows a list of qualifications for the partner).
The three samadhis are Shurangama, Vajropama and Mayopama samadhi, besides them there are hundreds of samadhis that are mentioned in the Mahayana. The term "awakening" includes hundreds of different things, it includes the fantastic qualities of the ten bodhisattva levels, and it includes the three or four kayas of a complete Buddha. You don't need to practice the so called "tantric sex" for all of these.
Even in the case of Shakyamuni or bodhisattva Siddhartha, because during his youth he enjoyed women, he had according to Etienne Lamotte three wives and two thousand concubines, there must have been an element sexual experience as a basis in his following years of meditation and ascetism.