I just got my DT 770 32 Ohms and I wanted to know more information about mass loading the drivers and damping. I was looking at this but am unsure as to what exactly this does. http://customcans.co.uk/s/s/index.php/acessories/beyerdynamic/dt770-mass-loading-mod.html
The idea is to give more bass detail with the extra mass and make them sound less boxy by absorbing the more of the sound coming off the back of the driver so less bounces back through. The kit was designed and tested on the the 80 and 250 ohm versions - in the 80 we recommend also covering the bass port with tape as they are a bit bass heavy. Unfortunately I have not tried it on the 32ohm version but the theory is the same.
Whether it is worth it or not is something I can't really comment on as I did all the design and testing on the kit originally so I am a bit biased
but if you are happy with the sound as they are then you won't need it, if you want to tweak them a bit then there is everything you need in the kit to have a play around and it can be removed without harming the headphones if you want to go back to stock