An excerpt from Guruji's Guru Stotram:
[Starting 0:53]
The Supreme Guru in our line is Dattātreya, who has written 11,000 upanishads, and who has given to the world 7 crores of mahāmantras, so he is the Mantra Śastra Supreme. He is Trinātha - Brahmā, Viṣṇu and Śiva, all together in one form and who is the Supreme Being.
There are two main Gurus in the Śrī Vidyā Upāsana, one is Dattātreya and the other is Dakṣiṇāmūrti. Dakṣiṇāmūrti is yourself and Dattātreya is a form of the Guru; there’s no distinction between these two. Dakṣiṇāmūrti is the Ardhanārīśvara form of Devi and Dattāreya is the Trinātha form of the Guru.
Dattātreya has given the external modes of worship. Dakṣiṇāmūrti has only concentrated on the internal modes of worship. This is the only difference. The external modes of worship are the route through which you learn the internal modes of worship. Without knowing what to do, how can you internalize the process? So first you need to know how to do the pūjā externally, then you can translate that into a mental action.
Source: Guruji compiled Guru Stotram
An excerpt from Guruji's 2013 Guru Purnima speech:
[So you see, a spanda, vibration or energy that we are familiar with]… in order to move at all, it has got to have a space in which to move, a time in which to move, and what moves. These three things. These things have been called trinity, trimurtis. And Guru Dattātreya is the manifestation of the Trinity.
They are asking questions, but he is not answering them. You are sitting there as a 16-year-old boy, nude, sitting under a papal tree, not answering questions. If there are questions being asked they are being answered within their minds. That is the wonder of Dakṣiṇāmūrti. Dakṣiṇāmūrti means, dakṣiṇa –means “right", amūrti – means “formless". The right part of you is formless. One part of you is formless, the other part has a form. Dakṣiṇa plus amūrti, Dakṣiṇāmūrti. Form and formless combined to have Dakṣiṇāmūrti.
And Dattātreya is a transition again between the form and formless. So these are two main Gurus of all kinds of vidyās. There are no other Gurus.
Source: Guruji's 2013 Guru Purnima Talk