Thanks for the ping.
I see I've missed a long and interesting thread.
I'm afraid right now I don't have time to fully participate, but I would suggest that all the posters, both Orthodox and Latin, might want to read the Tomus of 1285. It is the most refined statement on the procession of the Holy Spirit ever issued by an Orthodox council, and while it was a local council of the Great Church of Constantinople, it bears reading.
It has been argued by modern scholars that is provides the intellectual underpinnings for St. Gregory Palamas' defense of hesychasm and Uncreated Grace against the rationalist speculations of Barlaam the Calabrian (who, incidentally, died as a Cardinal of the Church of Rome).
The key point is, that while insisting that the Spirit proceeds from the Father (alone) (indeed it condemns the Acta of the Latin Council of Lyons for denying the traditional doctrine), it declares that the manifestation of the Spirit through the Son is not merely economical, but eternal.
I am puzzled by the one Latin poster talking using the word 'sequential' in connection with triadology. St. Athanasius' "There was not when the Son was not" applies equally to the Spirit. God is eternally Father, Son and Holy Spirit. There is no sequentiality in the atemporal and eternal causation (in two different modes--begottenness and procession) of the Son and the Spirit from the Father.
"Sequential" was my choice of words. I understand it is awkward because it suggests a time sequence, inapplicable here. I merely tried to underline the difference in how the Orthodox and the Catholics understand the relation of the persons in the Holy Trinity. The Catholic is "sequential" in the sense that the Father eternally begets the Son and the Holy Ghost proceeeds from the two. The Orthodox is that the Father eternally begets the Son and is the source of the procession of the Holy Ghost.
Can you please provide a web link for "Tomus of 1285"? I can't find it using search engines.