While doing some of my research for this website, I came across a Most Excellent resource covering the area of Headphones. Sean Olive - Research Fellow with Harman International - and his fellow scientists have been busy conducting all sorts of studies of Listener Preferences and how headphones should behave to produce the best listening experience. He has produced some interesting studies and videos that should interest everyone using headphones. I am providing a link to his blog page for your reference.
Thanks for all the hard work, Sean!
Sean Olive's Blog on Headphones and stuff here