Footsteps aren't playing. Also, the playback position isn't accurate.

I completely agree with your opinion.
 I've been using the Sennheiser IE 900 and FiiO K15, and I'm running into the exact same problem.
I don't think my ears are the problem because I could clearly hear footsteps in BFV.
 Is the audio configuration bad? A $1700 earphones and a $550 DAC/amp? It's unacceptable. This is a deep-seated issue that is making the gaming experience boring. I earnestly hope for a solution as soon as possible.