As I discuss in this question, the Sri Vaishnava sect (of which I am a member) places great importance on the Divya Desams, the 108 sacred places of Vishnu which are mentioned in the poems of the Alwars. Now two of the Divya Desams are not even on Earth! As I discuss here, there is Thiruparkadal, Vishnu's ocean of milk, and then there is Paramapadam, the abode of Para Vasudeva or the supreme Vishnu as well as the destination of those who have attained Moksha. (See my answer here for more information on Para Vasudeva.)
In any case, here is how the Sri Vaishnava Acharya HH Chinna Jeeyar Swami describes Paramapadam in one of his discourses:
Swamiji narrated the seating arrangement of Paravasudeva in Vaikuntam starting with Kurma (holy tortoise) forming the base on which Adisesha lies down as the bed hosting eight different demi-gods on 8 sides namely, Dharma, Adharma, Aiswarya, Anaiswarya, Jnana , Ajnana, Vairagya and Avairagya (each with three heads namely, Satva, Rajas and Tamas) and 12 different Ganas holding various weapons. All of these demi-gods hold a Lotus that hosts Simha Mukhas (Loin Faced demi-gods) on four corners and Sadasiva with 25 heads in the middle holding Bhadrasanam on which, Vaikuntanadha is seated with Sreedevi, Bhudevi and Neela devi. Vaikuntanadha holds a mudra with his right hand extending an invitation to all the souls to come to him. His left hand is placed on the ‘Bhadrasanam’ giving it the needed support. In the other two hands he holds the divine conch and the discuss like ornaments to assure his devotees that he is not exposed to the evil eye.
Bhadrasana refers to a sitting posture, but my question is, what scriptures describe Sadashiva carrying Vishnu in Paramapadam?
As you can see in the image above, how Paramapadam is usually depicted is with Vishnu sitting directly on his serpent couch along with his wives Lakshmi, Bhudevi, and Niladevi. But HH Chinna Jeeyar Swami seems to be saying that Sadashiva is on the serpent couch and then Vishnu and his wives are being carried by him.
I'm also surprised that Sadashiva is playing a role at all; as I discuss in this answer, in Shaivism Sadashiva denotes the supreme Shiva, whom Shaivites equate with Brahman. But Sri Vaishnavas believe that Para Vasudeva (the supreme Vishnu) is Brahman, and that Shiva is a Jiva, so what role could Sadashiva play? The only Vaishnavas I know of who acknowledge the existence of Sadashiva are the Gaudiya Vaishnavas, who believe on the basis on the Brahma Vaivarta Puranas that Sadashiva came from the body of Krishna.
On a side note, I found it strange that Sadashiva was described as 25-headed, when he's usually depicted as 5-headed as I discuss here. But this webpage says there is a so-called "Mahasadashiva" form, which has 25 heads relating to the 25 elements found in the Samkhya system. (24 elements of Prakriti plus Purusha.)