I completely understand. My parents were always very religious, and so when I entered Orthodoxy, they were quite hostile. Since then, though, they have come to realize that it is indeed Christian. They still think of it as the same as their Protestant denomination, but they are at least no longer hostile. I think this is in large part to my realization that they thought my going to another religion was a rejection of them. In fact, it was the fulfillment of what they were trying to teach me since I was very young.
My mother's main objection with the church was that she thought we redefined Christ to make him something He is not--a fine objection. Actually, the Orthodox doctrine of the Trinity is what I had been speaking with her about for years before I was Orthodox, and she now agrees that it's more accurate than her own church's (she feels her church limits the work of the Holy Spirit, and I agree). Since that first hurdle, she's been able to slowly integrate Orthodox ideas into her own theology, so that now she calls herself Bapticostodox. Okay, I can go with that. She's very much where I was shortly before converting.
My father's objection was that Orthodoxy made too big a deal of Mary the Theotokos. I've been careful to describe every theology we have about her as being about the Church as a whole, as she is an example for the Church of how to bear Christ to the world. He agrees with me that the Church ought to bear Christ, but is not yet convinced that those things apply to the Theotokos. I think eventually, though, he'll connect the two.
The thing my father liked best about Orthodoxy was the communion. He had complained for years that his church had stopped taking communion every week from the same cup and had gone to a once-a-month, Sunday-night communion with little plastic cups. In fact, as they were looking for a new church, Sunday morning communion was very high on his list. Unfortunately, the church they belong to now does not participate in that tradition, but he still holds it as a very high priority. That's an Orthodox idea.
So I guess the best advice is that as you convert, make sure that your parents know your conversion is not a rejection of them. As you can see, my parents taught me Orthodox things, even when they did not know these things are Orthodox. Try to find something similar with your parents, and it will ease the tension and maybe even improve your relationship.
Hope that helps.