Head tracking is completely unnecessary, unless you happen to listen with your head tilted. Head tracking attempts to add information that's not stored in the sound at all, which is in general impossible. The result is that the sound is colored (unless equalized, say hi to this thread) and has phase artifacts.
Note that the equalization and adjusting their head shadowing model is most of the personalization they're doing.
In other words, headphones equalized to sound flat to your ears + crossfeed set by your ears = >90% of their system sans head position sensitivity and phase artifacts.
Their head shadowing model is only slightly more advanced than spherical head - they use earlobe position on the head, which changes front-to-back frequency response difference. That's irrelevant for stereo, but relevant for surround sound and their positioning trick.
Crossfeed effect is not small - the reason it's small in certain implementations is that center frequency is set to some lowish Hz (I need 1800 Hz not some 300-900 Hz for proper positioning) and/or the amount is too low (I need 15 dB) and/or highboost is used. (for me, it moves the sound inside or behind the head)
BS2B can barely match these settings, esp. crossfeed amount.
Crossfeed synergizes with equalization greatly. I'd call it an exponential improvement of soundstaging when the two are combined. (crossfeed to the eq power)
Rockbox's crossfeed is known for being subpar. So is Foobar2000's old crossfeed. Head-fit is pretty decent - the nice part is that you can equalize in the same plugin, but its crossfeed colors the sound - but for me, BS2b and plugins derived from it are the winner. My own passive crossfeed circuit based on Linkwitz's comes pretty close to it.