Thanks for your concern about this area of theory. I discussed the empathic wall in Chapter 7 (pages 93-107) of my 1992 book "Shame and Pride: Affect, Sex, and the Birth of the Self," (WW Norton, New York and London) which is easily available in most parts of the world as an inexpensive paperback. (I would guess you are writing from Europe.) The concept was introduced in Nathanson, D.L.; The Empathic Wall and the Ecology of Affect; Psychoanalytic Study of the Child 41:171-187, 1986. The mechanisms for interaffectivity are spelled out there quite well.
As for the question whether any affect, or the later derived script we call an emotion, is or is not biological, should you read Shame and Pride, you will appreciate that I have suggested that everything we can learn about emotion must be a matter of hardware, firmware, or software. Unless we take such a position, we must be forever locked in mysticism and untestable hypotheses.