The non-Chalcedonian Orthodox have a different understanding of “nature” than do the Chalcedonians, I think. For the OO, to say that Christ is “in” two natures rather than “from two natures” (the two natures which become one in the incarnate Word) sounds like Nestorianism in that it divides the one person of Christ into two, with one doing all the human stuff, and the other doing all the divine stuff. Now, I know that’s not what modern Chalcedonians believe (having been one, after all), but reading certain passages from the Tome of Leo about how “the divinity receives praises, the flesh receives insults” or what have you really, really sound like it. This is an important thing to understand in the OO-EO divide: Neither side wants to be seen as supporting something heretical, so we balk at accepting things that seem Nestorian (as theChalcedonian Christology seems to the OO), or Eutychian (as the non-Chalcedonian Christology seems to the EO). It’s not about trying to neutralize differences (in other words, we’d rather reject Chalcedon than compromise on it), but avoiding heresy.
I’m not really sure what more to say about this. Chalcedonian Christology, whether coming from Rome or the Chalcedonian Orthodox, is Chalcedonian. We simply don’t agree. What specific differences do you want me to look at?
I don’t know what site to recommend on this issue, as it’s not really the kind of thing that can be sufficiently dealt with in a webpage. There are a few books on the subject of Chalcedon from the OO, but most are not in English. It’s not a quick read, but it’s a bit easier than Fr. V.C. Samuel’s “The Council of Chalcedon Reconsidered”, which is probably the best/most scholarly treatment of Chalcedon from an OO perspective (Fr. Samuel was a Syriac Orthodox priest from India):
Coptic Interpretations of the Fourth Ecumenical Council by Fr. Matthias F. Wahba of St. Atonious COC, Hayward CA.