Once you’ve got that all order, to put a cherry on top it would be ideal for the amp to play nice with my laptops (PC at work, Mac at home) *and* my *iPhone* 4S. I haven’t found a headunit that works with PCs and iDevices. If one doesn’t exist it would be a big plus for the amp to include inputs so I can get digital sound out of my iPhone (with the Pure i20 or its ilk) and into my headphones.
Magnetostriction headphones, sometimes sold under the label Bonephones, work by vibrating against the side of head, transmitting sound via bone conduction. This is particularly helpful in situations where the ears must be unobstructed, or for people who are deaf for reasons that don't affect the nervous apparatus of hearing. Magnetostriction headphones though, are limited in their fidelity compared to conventional headphones that rely on the normal workings of the ear. Additionally, in the early 1990s, a French company called Plasmasonics tried to market a plasma-ionisation headphone. There are no known functioning examples left.
Earbuds have small speakers that rest on the ear canal of the wearer. These are usually much less expensive than on-ear and over-ear headphones and reproduce the sound well. However, outside sounds, such as traffic or power tools, can get past the earbuds and interfere with your enjoyment. Earbuds also don't stay in place very well if the wearer is moving much, such as exercising. These also are lower fidelity than on-ear and over-ear headphones.