I am comparing to processed digital audio in 7.1 while wearing closed back headphone that can give feeling of depth and height and audible frequency separation (practically I have felt 7.1 audio through my Closed Back Headphone)
Is an open back headphone with un-amped, un-processed stereo able to give a feeling of depth (front to back), height and width of an “object location” and realistic sound separation with just two speakers?
If the source signal is a binaural stereo recording that happens to match well with your own head and torso related transfer function (HRTF), then you can get a fairly good front-back, depth, width and sense of space (echo, reverbation) sense using stereo headphones, be those open or closed headphones.
However if your recording or sound source is plain old stereo microphone, then the illusion of space is usually greatly diminished.
No headphone, using any 7.1 source material and processing that into any 3D stereo sound is able to convincingly create an illusion of height (up-down) at least not for me. The 10.2 surround sound (and 12.2) format(s) has also height information, but I haven't heard a system that is able process this type of signal into headphones without losing the height information.