The main problem? These cans grip your head like some sort of life-sized vice-grip, and don't let off. Many people have reluctantly returned them because of this major comfort issue. But, albeit with some research, here is how you can release the grip and make these cans much more comfortable.
Mod #1: Stretch the band out to release death-grip!
Step 1: Make sure the pads are facing one another and touching.
Step 2: Pull off the rubber on the headband (pulls back on when done), and reveal the metal band printed with “AKG”.
Step 3: Under the white lettering saying K81DJ on the headband, use both hands on both sides to push each side of the headband towards each other. You’ll notice the metal at the top bending and if you do it excessively forming a little hump.
Step 4: When finished and satisfied, pull the rubber back on from step one, and voila!
Covering the both drivers, there is a very thick foam pad. Problem with this is that it absorbs frequency and muffles the treble and mids of the K81s significantly. So simply remove the foam pads and the clarity will increase greatly, you’ll hear the difference.