Sorry to dig up a very old thread, but I think there is no point in opening a new one since my question is directly related to this one.
I've recently bought these headphones and tried the aluminium only, aluminium + center foam, aluminium + cotton pads, aluminium + cardboard and also center foam + cardboard.
This were attempts to reduce the bass distortion at high volumes in bass tracks, but all pretty much failed. The most noticeable difference were the aluminium mods, that brightened up the highs. However, I did find them very harsh when modded.
However IMHO I do not find the highs unexistant or recessed. It's quite the opposite: the headphones sound surprisingly well balanced, excepting for the highs. I often find myself lowering everything above 4Khz just a little. Did Sennheiser made any changes to the headphones recently?
Probably I should just wait till I get 100hours of burn-in, since they have been only playing for about 20 hours at moderately high volumes. Has anyone tried any other combinations trying to solve this?