Orthodox epistemology: We can know what's absolutely true through the Scriptures, the liturgical traditions, the hymns, the icons, the testimony of the Fathers, prayer, fasting, theosis, and all that God offers to the Church!
Which I would say are part of the church's ordinary magisterium. (We include all the Eastern traditions; the non-Catholic East really doesn't include the Western. Western Rite Orthodoxy is self-limiting because the Orthodox don't really want it. To be Orthodox is to be Byzantine.) The extraordinary magisterium (a council or a Pope defining a doctrine) is very rarely used, and can't contradict defined doctrine; that is, it can't invent new doctrine as non-Catholic Eastern theologians and Protestants accuse. And even when it's used, it's used very cautiously to define what Catholics already believe: Mary is all-holy and was assumed into heaven (both of which Orthodox really believe too) and that the Pope's office, not the man, is infallible when defining doctrine. For example, Catholicism's latest council, Vatican II, didn't define any doctrine. It repeated what's been defined and made some policy changes. The church can translate (part of, as the council really said) the services, drop the office of Prime, have official talks with the East and with Protestants, and tell Roman Rite Catholics they can eat meat on Fridays most of the year, but it can't ordain women, marry two men, or say divorce and remarriage is OK. (We can't change the matter of a sacrament or say adultery is ever right. Much of Catholicism is really about what the Pope can't do!)
If everything you're saying here is true, then the standard Catholic, presuppositional apologetic appeal to "final authority" falls flat, for the argument implies that the Orthodox Church cannot provide the laymen certainty about absolute truth, just because it doesn't have an infallible Pope who has the "final say." Am I right to conclude that you believe in Catholicism, yet agree with me that this apologetic should not be used as a "silver bullet" argument for Catholicism against Orthodoxy?