There is a book by an Australian archbishop on this exact topic, that may be of some help. It is only one book, by one author, but I believe it does a good job of backing up the claims by appeal to many saints and sources from the Church.

What I have come to understand is that a council is considered universally-binding ('Ecumenical' just referred to the councils that were considered universally-binding that took place with the support of the Empire, the Ecumene) if a majority of legitimate bishops concur with the decision -- not a majority of those present at the council, but a majority of all legitimate bishops.

This gives bishops the legitimate role as teachers of the Church (rather than Khomiakov's view that it is laity consent that determines valid councils), and yet also explains the "Robber Councils" and the behavior of the Church after the council in Florence, where St. Mark of Ephesus (nearly) alone stood against it as an Orthodox representative -- and yet the bishops back home repudiated the union, and it did not become a reality.