Finally got around to prototyping my head amp. Its comprised of a discrete op amp driving a diamond buffer output stage. The sound is awesome considering its all on a breadboard and shortcuts were taken due to limited breadboard space. Id like to expand the input section to include defeatable tone controls and proper input filtering and protection. What I have right now is mostly just the gain stage and output stage. Ive also played around with taking feedback globally, enclosing the diamond buffer output stage in the feedback loop, as well as closing the loop ahead of it - and leaving it out of the loop. Ive created a page on my website with lots of pictures and a schematic. In the mean time, here is a photo -
http://sparkoslabs.com/headphone-amplifier/