The Parameswara (God) himself gave to his Avatara five Spatika Lingas and commanded him to have them installed in five places and arrange for the pooja. In carrying out this command, the Acharya installed in both his Mutts, here in Kanchi and in Sringeri, two of the Spatika Lingas.
Thus the Lingas that Parameswara himself had given and installed in these two places for which poojas were arranged became the central deities of worship in these Mutts and other deities became parivara deities.
In the remaining Mutts also, for the sake "uniformity", the Acharya had necessarily to make the pooja arrangement as Siva Panchayatana.
Now you may ask: You said that Acharya, when he wrote Bhashyas which were books on Atma Sastra, was only in "Atma Swarupa" and had no "identity"; if he was "Atma Swarupa" , and remained as such, then why should he identify with Siva Avatara, and therefore think about "not talking about himself" and therefore think about using the NARAYANA name.
I knew such a question can arise. I have my answer ready. I came to talk about this with a question paper and a answer sheet, all prepared.So, what is the answer? The answer is that "Atma Swarupam" will not write books. In fact, it does not do anything.
It will just be as it is. It will not act or do. The moment he sat down to write, it means that the "Atma Swarupa" has yielded to place to Avatara. To be correct, the Samadhi state of Atma Sakshatkara is over, and the thought of having to perform a "duty" for the up-liftment of Dharma in this world for which this Avatara came makes him to sit down to write.
In that movement, the question arises, Avatara means whose Avatara. When you get the reply Siva Avatara, it follows that Avatara Siva talking about Adhara Siva does not look proper and talking about Vishnu appears more graceful, balanced and dignified. Is that not so? So it is, in the Bhashya books, the root (moola) of the causal principle of the Jagat is referred to by the name Narayana.
The supreme central meaning of these books is the Oneness (unity) of Paramatma and Jivatma, that is Advaita. In this way, the use by Siva Avatara Acharya of Vishnu's name brings in the Hari Hara Advaita - that Siva and Vishnu are one and the same. Mahavishnu has many names.
In fact, there are a thousand names. Then it may be asked why the Narayana name is chosen. The supreme astakshari mantra of Mahavishnu has the Narayana name in it.