It might be an idea to take a step back and just look at the two audio sections without being too constrained by the video. Obviously, you can't move the transition too far from your cut, but sometimes you'll find a perfect transition point that's just a little further back or ahead that either necessitates a slight trim to the footage, or filling the gap with something else.

I too have used the Howard Shore OST's in my project, and many times, I've got the audio right, only to find that there's then a small gap in my video that I never intended. Obviously as faneditors, our situation is rather unique, as any regular editor wouldn't be constrained in this way as they'd have access to the source video, but following these rules does ensure the product ends up far more polished. There's a generally held belief that audio is more important than video, and I happen to believe that's true. Our brains, are very good at detecting when something doesn't sound right. It's far more forgiving when it comes to visuals.