Really Good Headphones

OLC question mark

The thread starts as follows: "So how far can one go? I've had some HD600s for a few years and I now have a very decent headphone amp too (or so I'm told). Since I currently have no access to decent speakers*, I've been pretty much on phones full time. They sound OK, fairly detailed, but bass extension is a bit limited. Am I asking too much? What can a really good 'phone do? "