I don't mind the darker cabinets because it helps your feature, the fireplace stand out. If you make the cabinets lighter, then they will compete with the fireplace.

Maybe you can stick light, bright wall paper on the back?

Agree with cpartist. I like the idea of using white/light items on the shelves against the dark background. White will also tie in with the fireplace and trim. Use a few larger items for the shelves, and maybe place all the small photos (or at least some of them) elsewhere. Keep the shelf decor simple for a nice, calming look.