asya sri vishNOr divya sahasranAma stotra mahA mantrasya|
sri vedavyAso bhagavAn RshiH|
sri mahAvishNu paramAtmA sriman nArAyaNo devatA|
Of the great mantra called the Sri Vishnor Divya Sahasranama Stotra, the sage [who heard it from the gods] is Sri Vedavyasa Bhagavan, the meter is Anushtup, the deity [whom it is about] is Sri Mahavishnu Paramatma Sriman Narayana.
My question is about the unusually elaborate epithet used for Vishnu, "Sri Mahavishnu Paramatma Sriman Narayana." The meaning is clear: Mahavishnu just means the great Vishnu; Paramatma means the supreme soul or supersoul, which Vishnu certainly is; and Sriman Narayana is a common name of Vishnu which means the one who sleeps in the water. But I'm wondering why this particular combination of names was used as the name of the deity of Sahasranamam. Usually when the deity of a mantra is given, a very simple name is used, so it might say "vishNu devatA" or "mahavishNu devatA" or "sriman nArAyaNo devatA".
Is this particular phrase something that occurs elsewhere to describe Vishnu, perhaps in the preamble of some of other mantras to Vishnu? Or is it unique to the preamble of the Vishnu Sahasranama?