Although I'm not sure I would guess the similarities might be like the difference in Sophia 1 & 2's with the tweeter being the dif.
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I believe the Series 2 has the same mid range drivers as the Sophia 2, but uses the Titanium tweeter of the Sasha, Max, etc. The Series 1 had a different mid, and I am not sure about the tweeter. It might have been a berylium like the current Sophia 2.
Hopefully someone answers this because I have wondered the same thing.