Same story with us although we've been to Ocho and Treasure Beach. We split Portland and Negril this Feb and had a great time in both. There is a bunch of info on Port Antonio on that thread on this page. We flew TimAir MoBay to Port Antonio then from there to Negril. Very expensive but the views are amazing - you get a totally different perspective of the topography of this beautiful country and the trip takes around an hour. Here's some video taking off from Ken Jones in Portland.

https://www.youtube.com/watch?v=wY6z8O0f3b8