It will take some time to respond adequately, as you can imagine. I will limit myself to a couple of points for now.
First, we Orthodox see neo-Platonism primarily in the Trinitarian theology of St. Augustine. His work "On the Trinity," which lays the groundwork for the filioque, is seen as an attempt to express the Trinity in neo-Platonic terms.
Second, you write: "That negative theology is the cornerstone of Orthodoxy would seem to be non-controversial and that it originates from Greek philosophy."
It is hardly the cornerstone of Orthodox theology. As I mention in my other post, it is a way of talking about God -- specifically the characteristics of God.
The cornerstone of Orthodox theology is our understanding of Trinitarian and Christologic theology. Most of this is made up of positive statements based on the revealed truth of Scripture and the living revelation of the existence of the God-man Jesus Christ.
If you will examine most Western systematic theology (Orthodoxy doesn't even have the concept of systematic theology, rejecting the idea that revealed truth can be systematized), the characteristics of God come right up front. For us, they are afterthoughts and implications. Greek philosophy is hardly needed to engage in such afterthoughts, nor is it the source of any way of approaching them. In fact, the point at issue in the Palamite controversies (our emphatic rejection of Renaissance thought, which was grounded in pagan philosophy) is the fact that the point of our spiritual lives is not knowing *about* God (i.e. his characteristics), but in directly knowing God and participating in his life through grace (i.e. his energies). Again, this is all personal and direct, not abstract.
What is up front in our theology is the direct revelation of God in the person of Jesus Christ: "he who has seen me has seen the Father."
How is it possible to say that it is impossible to know God positively when we have seen Jesus Christ? What do you think the iconoclastic controversy was about? We are so concerned about the particularity of the revelation of the Incarnation that we believe iconoclasm to be a subtle (and sometimes overt) denial of the fact that the God-man Jesus Christ walked the earth and that he will return again to earth in that same body. We portray him not as he was, but as he *is.*
I would specifically point out that Orthodoxy completely rejects the idea of an abstract unity, whether of "the One" or of God. What do you think the filioque controversy was all about? Orthodoxy sees the unity of the Trinity as being not some "God in general" or abstract "Godhead," but we see the unity of the Trinity as being based in a *person* that we can know, worship, love, and relate to: the Father. "I believe in one God, the Father Almighty..." The Father is unbegotten and does not proceed. The Son is begotten of the Father before all ages, and the Spirit proceeds from the Father (as Christ himself said.) Father, Son, and Holy Spirit are equally without beginning, and equally God. The Father is the source of unity in the Trinity, and he is a person, not an abstract essence or Godhead.
We can know God only in a personal way -- through the persons of the Father, Son, and Holy Spirit. The filioque eliminated the Father as the personal focus of unity in the Holy Trinity, and created an abstract Trinitarianism and a language about God that was abstract. We see its fruits all around us today in the West.
Look at Orthodox services -- how we worship. It is all personal -- Father, Son, and Holy Spirit. You will be hard pressed to find a "God in general" -- let alone a "One," in any form at all, in the way we worship. And we repeatedly say and believe to the core of our being that what we pray *is* what we believe.
It is absolutely a misapprehension of what Orthodox Christians believe and practice to think that some sort of process of negation or abstraction is going on. It is precisely the characteristic abstraction of Western theology that started with St. Augustine that we find incompatible with Orthodox Christianity.
What *do* they teach in the schools these days? :-)
More later.