If you want to see what the Orthdoox Church teaches, look at her liturgical services, which are lengthy, detailed, and ancient.
I have written on this at length elsewhere. The services of the Orthodox Church for the feast of the Dormition are dominated by language about the Theotokos dying, and about Christ receiving her soul. This is depicted in every icon of the Dormition, with Christ holding an infant Theotokos in his arms, representing her soul, and a dead or dying Theotokos lying in the midst of the Apostles.
The second most common thing talked about is her "translation" from earth to heaven. The language is ambiguous -- sometimes it is clearly talking about her soul, at other times it could conceivably be her body. There are a few references in the services, though, that seem to indicate that she was taken up bodily into heaven. But even these are not crystal-clear -- and usually, when the Orthodox Church is talking about a dogma, the services are not only crystal-clear, but they approach it explicitly from so many directions that you really can't mistake it.
For instance, if one looks at the service for the Annunciation, just finished (and at the icon) -- Christ's bodily Ascension into heaven couldn't be more explicitly spelled out. There just isn't anything like that about the Theotokos.
I personally think that the witness of the Orthodox Church's tradition points to the Theotokos being resurrected and brought to heaven to be united with her soul, but it is not by any stretch the central message of the feast we commemorate on August 15.
Regarding the Immaculate Conception, I would need to see the exact quotations, in context, from St. Photius before I would believe that there was this teaching coming from him. There appears to be confusing in the Catholic Church regarding what the feast of the Conception of the Theotokos means and meant to the Orthodox. Both canons in the service for this feast are canons "of Anna," and at least the first one dates back to the 700's.
There is nothing in the services that could remotely be construed as reflecting the teaching of the Immaculate Conception, other than one hymn that speaks of the incorrupt womb of the Virgin and the corrupt womb of Anna. This would really be stretching it, since the obvious explanation is that the Theotokos lived a morally guiltless life, and that her womb was sanctified by the bodily presence of Christ, whereas we could say neither of St. Anna.
The manuscript tradition is so old, and the conservatism of our service books so great, that one can only assume that this means the Church didn't teach the IC. If it were taught, it would be at least mentioned in the service -- even if only as obliquely and ambiguously as the bodily assumption of the Theotokos is mentioned on the feast of 15 August. But rather, the miracle of the conception of the Theotokos by St. Anna that fills every corner of the services is her miraculous conception by parents too old to conceive.
This has implications, since Pius IX appeals to the Eastern origin of the feast of the Conception of the Theotokos (quite true), and furthermore he said that only two conceptions are commemorated by the Church. This is, as any Orthodox Christian, not true, since the equally miraculous conception (also by parents too old to conceive) of St. John the Baptist has its own feast in September -- a feast which homiletical evidence shows existed at least by the 5th century in the Church of Jerusalem. The main hymnography in our services date to the 700's and 800's.
My point is simply that Augustine hadn't even been translated into Greek before the fourteenth century (Fr. Romanides says this IIRC) - I doubt that a belief in the IC among post-Photian Greek authors can be attributed to Western influence. When the Feast of the Conception of the Mother of God was introduced into the West, it was immediately opposed on the basis of rejection of the IC, so it seems a bit strange that in the East it could never have carried any suggestions of the IC.
You are right that Pius IX gets it wrong in "Ineffabilis Deus":
"By this most significant fact, the Church made it clear indeed that the conception of Mary is to be venerated as something extraordinary, wonderful, eminently holy, and different from the conception of all other human beings -- for the Church celebrates only the feast days of the saints."
- all the more strange since St. John the Baptist's conception was also commemorated in the Western calendar.
The Catholic Encyclopedia argues that the IC implied in the feast of her conception: "In the Office of 9 December, however, Mary, from the time of her conception, is called beautiful, pure, holy, just, etc., terms never used in the Office of 23 September (sc. of St. John the Baptist)". Do you suppose that might have any basis?