I've been and still using beyer gels on a DBV-like mod without much problem. I don't really recall precisely how they sounded initially, before the first adjustments, but now their sound doesn't produce any fatigue. Granted, I do listen with stereo convolution plugin, which makes the sound significantly more comfortable, but even before I've started using that plugin, the sound was bright, but not fatiguing.
Initially, I've attached them using electician tape, and stuffed cotton into chamber between baffle and pad around the opening. The sound was fatiguing, with spikes in lower treble, and I've added acoustic foam lining on the earpad opening, which improved things greatly, but there were still some ocassional spikes. I have slapped a chunk of foam over the center square of the driver, which fixed things.
Not so long ago, I grew tired of tape attachment, as it precluded easy opening\closing of the headphones, and made lips out of pleather, and attached them to pads with rubber cement. As a result, pads became angled (it was intentional) and much further spaced from the headphone than with tight tape attachment. I still used cotton under the pad, foam lining and foam on driver center. I've also added the foam circle from pads' package, so that the now-loose cotton would stay in place. The sound didn't change much, to my surprise. Imaging has improved somewhat, and feeling of pressure upon eardrum, which was making previous iteration somewhat uncomfortable for long listening, has vanished completely - now my ears don't feel the presence of headphones, it's just like some open phone with velour pads. Isolation was also reduced, but I tend to think that's not due to isolation, but that because now presence of headphones doesn't trigger ear safety reflex - I recall hearing noise in my ears with tape attachment, and nearly no noise at all with proper lips. I'm happy with them.
On the measurements side, my current setup is pretty flat, with +10db buildup of lowest bass (20-30hz) even despite having nearly everything closed( they do have a baffle port, but everything else is closed either with plasticine or electric tape.