I own the ER-4P's and they're very good. Of all the earphones out there (in-ear and regular earbuds) they are at the topic for balanced response. To get the best out of these, as with any high-end ear/headphones, you should listen to them through an amp. The ER4-P's need a small adapter that changes the impedance, or ohms, to make them match the amp--the ER-4S are made for an amp without that tiny adapter, but don't work as well with a self-amped device like an iPod.
Google "binaural recording" or something and give some of the free samples out there a listen with whatever set of headphones you have lying around. Find some music suitable for binaural recording (big bands/anything electronic or amplified = not very suitable, but solo instrument = wow) and close your eyes. It's fun.
I don't know if I read your post carefully, but if you suggested some kind of switch mechanism that would let the output switch between amped and line--well, that would be awesome.
About the Bithead, it really shouldn't need proprietary drivers on any modern system. It's just an outboard DAC (digital-to-analogue converter), which is one of the most simple and standard kinds of chips out there. It doesn't need a signal sent to it in any special way; it just receives the audio stream digitally over USB and the DAC converts it to an analogue signal. Done.