[AlguyA]

'It really isn't accurate to speak of "the Septuagint" as one, bound, definitive text."

Indeed. However, doesn't the Septuagint roughly parallel what scholars call 'the Alexandrian canon?' Also, would it be fair to state that if one accepts as canonical the Palestinian canon upon which the Protestant Bible is based then one is forced to admit Matthew's emphasis on the Virgin-Birth of Jesus lacks support from Isaiah? Put simply, wouldn't there be a discrepency between the way Matthew qoutes the verse and the way the verse itself appears in Isaiah?

[malakhi]

However, doesn't the Septuagint roughly parallel what scholars call 'the Alexandrian canon?'

If by this you mean that diaspora Jews considered certain books inspired that were not held as inspired by the Judaean Jewish community (which used a stricter criteria), then yes.

Also, would it be fair to state that if one accepts as canonical the Palestinian canon upon which the Protestant Bible is based then one is forced to admit Matthew's emphasis on the Virgin-Birth of Jesus lacks support from Isaiah?

Yes and no. Even if you hold Isaiah 7:14 to be a prophecy of the birth of Jesus, the expression "young woman" does not preclude the woman in question from being a virgin.

Put simply, wouldn't there be a discrepency between the way Matthew qoutes the verse and the way the verse itself appears in Isaiah?

This is hardly the only discrepancy between the gospels and the Hebrew scriptures.