I actually found this thread after doing some googling for these headphones. I have made a modification that I believe helps the frequency response.
One of the mods people at Head Fi have discussed is to cover the inside of the cup with dynamat. This supposedly alleviates the bass resonance issues and cleans up the overall sound signature. I tried this initially, but found that it just kinda killed the sound. I then tried different arrangement/sizes of butyl rubber and foam, but none of them were completely satisfactory.
I decided to give it one last try by applying four small squares of butyl rubber on the largest pieces of carbon fiber on the inside of each ear cup. Here's a quick diagram I threw together:
To my ear, this results in a dramatic reduction in low-end resonance without really negatively impacting the rest of the sound signature. Unfortunately, I don't have a way to measure them so I'm basing this purely on my listening. I still think they benefit from EQ, but not nearly as much as before.