"Previously I'd just assumed that all the Orthodox pretty well feel salvation only lies in the Orthodox church. I didn't realize there was as much confusion/question on the issue as the book suggests."
I don't think its confusion but rather more simply a matter of simply leaving a mystery a mystery, rather like the "mechanics" of the bread and wine becoming the Body and Blood of Christ at the Divine Liturgy. Its just not something we speculate on because we literally don't know. There are, as I said, some who maintain that there is no theosis outside the bounds of the Orthodox Church, but they tend to be Orthodox versions of the Latin Church's sede vacantists. Many (but not all) belong to the various "One True, Honest to Goodness, Real Orthodox Church", or variations of the same.
By the way, most anything by +Kallistos is a good read to someone with a Western mindset.
Good points.