The different purusa-avataras are described in Satvata Tantra:
"The original Visnu - Sankarsana has three forms called purusas. The first, Maha-Visnu, is the creator of the total material energy (mahat tattva), the second is Garbhodakasayi, who is situated within each universe, and the third is Ksirodakasayi, who lives in the heart of every living being. He who knows these becomes liberated from the cluthes of maya."
Commentary by Srila Vedanta Acarya Baladeva Vidyabhusana
"The creator of the mahat-tattva is the antaryami of prakrti called Sankarsna (Maha Visnu).
The second is the antaryami of Brahma and is called Pradyumna (Garbhodakasayi Visnu).
The third is the antaryami of all jivas and is called Aniruddha (Ksirodakasyi Visnu)."
(Laghu Bhagavatamrta 2.9 - Srila Rupa Goswami)
