Reviving this old thread to share that I recently got a used pair of these on Amazon: http://www.amazon.com/Aftershokz-AS301-Wraparound-Headphones-Conduction/dp/B007003J2E/ref=sr_1_4?s=electronics&ie=UTF8&qid=1399220311&sr=1-4&keywords=aftershokz
They work more like the Echofone in that they transmit sound through the facial bones to your inner ear. I hooked them up with the left and right channels reversed by using a pair of 1/8" to RCA adapters (one with male plugs and one with all female plugs) only with the red plugs hooked to the white plugs to switch the channels. I also included a 12db in-line attenuator to reduce the volume as it works best if the Aftershokz is lower in volume than the headphones, but an external inline volume control would work also. Here is what I used because I had them on hand: http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_2?s=electronics&ie=UTF8&qid=1399221290&sr=1-2&keywords=12db+attenuator
I am using them off of the extra headphone output on my Tera while the other headphone out feeds my iCAN Nano amp and my JVC HA-FX850 iems. The effect is very nice with a bit of crossfeed effect again. I mostly notice a more realistic sounding depth to the image and maybe a bit more instrument separation. There is also more of a 3D quality to the sound: without the Aftershokz, the sound is more 2 dimensional and a bit flat. With the Aftershokz, there is more of a sense of say a real 3 dimensional human body singing in front of me. There is also a bit more fullness to the sound even when I compare with the volume equalized to account for the added volume with the Aftershokz turned on.
The other quality is harder to describe, but the Aftershokz do vibrate the skin and bones instead of the ear drum. So when I combine them with my headphones, there is more the sense of involving my body in the experience. It is not the same as when your whole body is vibrated by the bass frequencies at a concert or with a powerful subwoofer, but it still shifts the experience from being totally in my head to feeling a bit more involving of my whole body.
The effect is subtle, but more noticeable than when I was using two regular headphones as described in the rest of this thread. And it is more noticeable on some songs than others, which may be due in large part because the volume of the Aftershokz is staying the same when I turn up the volume on the Nano amp feeding my regular headphones. So when I turn up the volume on a quieter piece of music the volume of my headphones increases, but the volume of the Aftershokz does not. I will experiment some today with just listening out of the Tera, and so then when I turn the volume up or down, it will go up and down in both the headphones and the Aftershokz.