I suggest you get a copy of something like Sony Vegas Pro, adobe premier, or Final Cut Pro, which will allow you to control sound balance as well as execute some basic video effects, like post-production motion blur, camera shaking, or lighting effects.
If you have any experience with photoshop and it's layers you'll understand how Vegas works very quickly. I'd like to help out, but I can't promise anything.
Do you think you could link me up with a copy of the original video, breathing sounds, and echo-roar sound? I could make something pretty quickly that sums up what you can do with Sony Vegas.
On second thought, if there was no breathing than that would leave the majority of the video silence wouldn't it? Maybe that could just be filled in with footsteps or something
This. I think grass step sounds from Slender or Minecraft, coupled with solid floor steps (also can be taken from MC) would do very nicely.