These hypostases are described as follows
"First Absolute - Tat. The Absolute Transcendent, the Supreme, Paratpara, (containing all, limited by nothing).
Second Absolute - Sat. The supreme self-contained absolute Existence, Sachchidananda, (Ananda uniting Sat and Chit), holding in its absolute unity the dual Principle (He and She, sah and sa) and the fourfoid Principle, OM with its four states as one.
Third Absolute - Aditi - M [the Mother]. Aditi is the indivisible consciousness, force and Ananda of the Supreme; M [the Mother], its living dynamis, the supreme Love, Wisdom, Power. Adya-Shakti of the Tantra = Parabrahman.
Fourth Absolute - Parameshwara of the Gita = Parameshwari of the Tantra "
Elsewhere in the same notebook -
The Absolute Unmanifested - Parabrahman, Purushottama, Parameshwara (holding in himself the Parashakti and in her the All).
SAT. The Existent (I am).
The Absolute containing all the power of the manifestation. The Absolute is Parabrahman-Mahamaya. The Absolute is Purushottama=Paraprakriti. The Absolute is Parameshwara-Adya (original) Parashakti.
...OM is the manifestation. The Mahashakti comes forth from the Supreme for creation. In the eternal manifestation the Two in One are evident to each other; their identity and union are foundation of the diversity of this play and it is the possession of this truth that makes the manifestation stable and eternal."
The description of OM that Sri Aurobindo gives is based on the four-fold arrangement of the Mandukya Upanishad. He then adds (referring to the supramental yoga)
"All this (first in the Upanishads) is the viewpoint from the mental consciousness. It is incomplete because two things that are one have been left out, the Personal Manifestation and the name of the Mahashakti. The subsequent growth of spiritual knowledge has brought about a constant effort to add these missing elements.
When the hidden secret has been discovered and made effective, the human consciousness will be exceeded,
the superconscient made conscient
and the subconscient or inconscient, which is the inevitable shadow of the superconscient, filled with the true spiritual and supramental consciousness.
The Trance, Dream and Waking States [of the Mandukya] (all imperfect at present and either touched with obscurity or limited) become each completely conscious and the walls, gaps or reversals of consciousness that intervene between them are demolished.
Tat then will appear in its entire truth, the Supreme Absolute, One in Two, each entirely in the other and both one in an ineffable Existence, Consciousness and Ananda.
Sat is the eternal infinite truth of Sachchidananda ready for manifestation. It is the One Existence, but the Two in One are there, each in each, each perfect in the other."
The above pertains to the Unmanifest Absolute Reality. This, in the form of "The concealed Avyakta Supreme" (i.e.Avyakta Paratpara), self-involved Sachchidananda, Parabrahman" generates the eternal and perfect transcendent manifestation.