You can watch the video below ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-zq5sU8BKHps.html ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-EUBMdh8jCeM.html
As much as I understand..It's because lord Vishnu's this posture reflects the whole universe even multiverse too..And Om is considered to be the powerful voice which originates these multiverses.Hence they both are same only.