"Does Orthodoxy regard Koine Greek as accurately mapping reality more so, say, than Hebrew, and thus the LXX is a more accurate document than the original inspired Scriptures?"
Not exactly. I was told by an Orthodox priest that we Orthodox prefer the Septuagint for two reasons:
1) The oldest *extant* copies of the Old Testament are in Greek. Now I realize that the Torah has been copied down from generation to generation, but the oldest piece of papyrus we can get our hands on is written in Greek.
2) Regarding the prophecy of Daniel in which he foretells of the messiah, the Hebrew states "He shall be born of a young woman," while the Greek Septuagint states "He shall be born of a virgin."
So if you want to call the latter a "more accurate mapping of reality" then so be it, I guess...
Do other Orthodox on this list concur with my (admittedly secondhand) knowledge?
There's another issue:
3) All the Christian manuscripts of the OT are the LXX, or derived from it. The only exception is the Vulgate: Jerome took a Jewish Hebrew text and translated from that. The problem is that because that text had passed through Jewish (meaning those Hebrews who had rejected our Messiah) hands for several centuries, i.e. Jerome was not working from 1st century texts, it can still be said to be a Jewish text. He was criticized for doing so at the time.
In other words, the LXX was translated by those we would say were of the same Faith as us (symbolized by the legend of St. Symeon as being one of the translators, and his problem with the translation of "virgin" leading to him being told he would not die until he saw its fulfillment). Those Hebrews who accepted our Messiah continued to use the LXX and it Hebrew Vorlage (varient readings in the Dead Sea Scrolls agree with the LXX, as do some pre-Christian scraps of the OT elsewhere). Those who rejected Him used another text type, which was approved at Jamnia AFTER the birth of the Church. The Masoretic text dates after Chalcedon, for instance.
In other words, the LXX has never been outside of those whom we would consider outside the Faith, which is a problem for Protestants: if you trust our Church to copy the Scriptures (and the King James Version, for instance, depended on late manuscripts from the Orthodox Church copied well over a thousand years after the autographs: as a matter of fact, I don't think they predate the schism of 1054), why do you reject that Church's interpretation. How do you know that we didn't "change" anything?
Case in point: all Christian manuscripts of the Bible have the Anagignoskomena/Deuterocanonicals: none lack them. And in this we are proved right in that the Jewish Talmud expounds on Sirach (the Hebrew text has been found in the 1800s). The Jews celebrate Hannukkah although their rejection of Maccabbees has deprived them of scriptural warrent (1 Mac. 4:56–59) for doing so (and for our Fundamentalist friends, the Gospels record Our Lord celebrating it (John 10:22-24). And the Jewish translation of Theodotion, done centuries after the rise of the Church, includes the disputed books (in fact, his transaltion of Daniel was preferred over that of the LXX by the Church, and it includes the "additions" in the LXX but not in the Masoretic text). So one can follow the path of the Apostles, or that of the Pharisees, Sadducees and Scribes.