Were there other Guru biographies mentioned in the preface besides the 'Shri Sai Satcharita' and the works of Dasganu Maharaj?

Yes, the preface mentions several other Guru biographies. Chapter 0 identifies the 'Brihat or Thorale Guru Charitra' by Shri Saraswati Gangadhar as a famous and widely studied text. It also references a detailed, scholarly biography by Shri Samarth Sadguru Tembhe Swami alias Vasudevanand Saraswati Maharaj, which was filled with various poetic meters. Additionally, the text notes that Shri Samarth Sadguru Dattatreya Maharaj of Balekundri had also written a Guru biography, but at the time, it did not seem to have been printed or published.