Dummy head binaural recordings work perfectly for me. I can hear forwards, backwards, up, and down perfectly.
The only 5.1 -> headphone HRTF implementations I've heard that properly give directional cues mangle the sound so bad that it isn't worth it.
The technology I tried is intended to be used for real-time games. Individual game objects' audio samples and their positions are run through their filter, accounting for position and the material properties of nearby reflective surfaces (hard vs soft, solid vs semi-solid).
Is this fundamentally different to the implementations you've tried? It seems to me you're referring to '3D' implementations that take an already-mixed 4 channel source and try to jam that into a spatial 2 channel mix. That's the kind of technology that I think is pretty lame/useless as well...
If you have a chance to try out Visisonics tech, I think it'd be worth giving it a go if games are your thing. Seems like you definitely know a lot about the subject.
Problem is, I rarely meet a game that does (I think maybe I own one or two, but I can't remember which ones, which tells you what sort of impact those games made on me).
Being able to already have positional queues on a per sound basis is much different than downmixing 5.1. The technology isn't useless when all I want to do is watch a movie and be able to enjoy it with headphones without garbled audio.
Like I said above, you can downmix left, center, and right, and throw in a little sub, and get a stereo/headphone mix, but positional cues provided by surrounds are gone, and you can't just mix those in normally, the mix gets too confused.