Wow, I didn't read headfi for a couple of days, and this thread has doubled in length. Hevan, the bump in the back of the 598 earcup is, I believe, their 'sound reflector' thingy that apparently improves the imaging (positioning of sound) of the headphones. I've not seen any headphones from any other company with the same bump there, so you should be safe looking at other brands.
I have to chime in here. I own the HD555 which have the same housing construction as the HD598. The bump he is referring to is just the place where the headband hinge joins the earcup. Look at the outer design and you will see it corresponds to where the bumps are. Since the drivers are angled toward the ear for a forward soundstage, the baffle is much shallower in the front than in the rear. The wires for the right cup also run through this hinge, so the cover is a bit bigger than the hinge itself.
The "sound reflector" you're referring to is actually just a well known piece of foam that gets stuck into the lower models such as my HD555 to differentiate them from the HD595, kind of like factory underclocking. Removing the foam effectively yields a free upgrade.
I've never had any issue with comfort, and the HD5x5 and HD5x8 are generally known for their comfort. I guess they weren't the OP's cup of tea for either comfort or sound. Good luck with the Beyers in that case, and let us know what you think about them.
That's not the reason why a tube amp might sound warmer than a solid state. Warmth, as a description of the quantitative physical measurement of temperature has nothing to do with warmth as a description of the qualitative interpretation of sound.
Edited by thrillhaus - 9/19/11 at 11:57pm