Let me try again and then its off to bed. First, a quick observation. Your comment that we do not receive the Holy Spirit directly from God like Moses for example isn't borne out by the Eastern Fathers at all, for example St. Basil the Great, St Symeon the New Theolgian, St. Gregory of Nyssa, etc., but I think I know what you mean.
I think we can agree that God is essentially unknowable, ineffable and completely transcendant. The Trinity is of one ousia which is shared in by three hypostasia. God for the Eastern Fathers was always thought of as "Trinity" and that Trinity sent the Son, Who was "begotten of the Father before all Ages" for the salvation of the world. The Latin Fathers tended to look at God (as opposed to the ousia of the Father being shared with the Word and the Spirit) as a unique essence first and only thereafter of God as Trinity. In Latin theology, the divine hypostasia become really nothing more than expressions of the inner relations of the ousia of the Godhead. Now, if this were so, then the very existence of the Holy Spirit can only be defined and determined by its relations to both the Father and the Son. Logically then, filoque must be true and absolutley necessary because there could be no distinction between the Spirit and the Son unless the Spirit proceeded from the Son, and vice versa I suppose. The Greek Fathers viewed this doctrine as a form of Sabellianism wherein the hypostasia are merely "modes" of a unique "God". The Greek Fathers taught that the Father is the only source of the Deity, the Son having been begotten by Him and the Spirit "proceeding" from Him. Because the Son and the Spirit are "omoosios" with the Father, each has His own existence and function both in the inner reality of God and in the economy of theosis. Filioque, in this theology, which was the theology of the One Church for 800 odd years, reduces at least the Spirit (and perhaps even the Father and the Son too) to a mode of some different God than we worship .
Kolokotronis,
Please see above. I think you are insisting on real or imagined differences and tend to elevate a nuance to a level of an unsurmountable obstacle. But it is just not so. Here is, for example, quotes from St. Basil the Great:
"Through the Son, who is one, he [the Holy Spirit] is joined to the Father, one who is one, and by himself completes the Blessed Trinity" (The Holy Spirit 18:45 [A.D. 375]).I will reflect on it some more as well. Thank you for your elucidating post."[T]he goodness of [the divine] nature, the holiness of [that] nature, and the royal dignity reach from the Father through the only-begotten [Son] to the Holy Spirit. Since we confess the persons in this manner, there is no infringing upon the holy dogma of the monarchy" (ibid., 18:47).
(Source: catholic.com, the emphasis is mine)
>>I think we can agree that God is essentially unknowable<<
You presume too much. For a Catholic to believe this, he rejects defined dogma which is the action of a heretic. To say God is not knowable is one of the oldest heresies. It goes back to ancient times:
There is no truth/
Even if there was truth, it could not be knowable/
Even if it were knowable, it could not be communicated.
All three of these lies are entirely false.