You might remember that the original LXX was kept in the Library at Alexandria, so it is hardly surprising that we don't have it: the Library was damaged by riots of Coptic monks, and destroyed by the Muslims.
The fact is the Masorete, in terms of oldest extant manuscript, is about 700 years more recent than the LXX. It is simply a scholarly error to regard it as more 'authentic' than the LXX simply because it is in the same language as the hypothetical ur-text.
If you want to focus on Isaiah, go ahead, and join the Christ-denying Jews in removing the prophecy of Christ's virgin birth from the Scriptures. Yes, on that point, Qumran agrees with the Masorete.
But you still have to explain away the Hebrew copies of Tobit and Ecclesiasticus found at Qumran, and the fact that Genesis, Eziekiel, Proverbs and several other books have the reading of the LXX confirmed against that given in the Masorete by the Dead Sea Scrolls.
And I still haven't heard a reason for preferring textual transmission via anti-Christian rabbis to textual transmisison by Christ's Church. Will one be forthcoming?
But it is the same text with vowel points that was in Origen's first column, right? and it preceded his fifth column LXX which was being composed as he went along. The text that emerged from Jamnia was in Origen's first column and thus precedes the LXX that came from Origen by 200 years.
But you still have to explain away the Hebrew copies of Tobit and Ecclesiasticus found at Qumran
What??? just because something was found at Qumran we're supposed to put it in the canon of scripture. A lot of things were found there, should we put the rules of the religious sect living there in the canon as well???
and the fact that Genesis, Eziekiel, Proverbs and several other books have the reading of the LXX confirmed against that given in the Masorete by the Dead Sea Scrolls.
So what. They were bad Greek translations and were probably discarded by the community. What about all of the fragments in Hebrew from the DSS that confirm the readings of nearly every book of the OT as found in the Masoretic text.
Are you going to trust a translation over the original text??? Since when??? Should we do that with the Greek NT???? That must mean that one or all of those English translations are superior to the original Byzantine Greek, right???
And I still haven't heard a reason for preferring textual transmission via anti-Christian rabbis to textual transmisison by Christ's Church. Will one be forthcoming?
Those "anti-Christian rabbis" transmitted the text that God gave to them and that they faithfully protected and preserved, even though in that text were prophecies of a Messiah who they had rejected. The fact that all those Messianic prophecies and books were transmitted accurately is clear evidence that the Jews knew them to be such an integral part of the Scriptures that to remove them would be a sacrilege. And since they so faithfully with those passages that confirmed the religion of their opposition, then they could certainly be trusted with the rest of the neutral text.
You do believe Paul don't you? You do believe him when he says that "unto them [the Jews] were committed the oracles of God", don't you? Are you going to tell God that he made a mistake???