To mod your m50s:
1) pull of the pads
2) remove the screws
3) remove the foam plug @ the back driver (the pic is an srh440 driver but the concept is the same)
4) Add some fiberloft/polyfill into the cups (equal amounts in both cups-I would use half the amount that you would think you need & make sure you pull on the fiberloft to separate it well)
For better isolation (optional):
1) unscrew the retention clips that retain the large felt disk
2) dynamat the cup
3)Reinstall the felt disk
4) Add some fiberloft/polyfill into the cups (equal amounts in both cups-I would use half the amount that you would think you need & make sure you pull on the fiberloft to separate it well)
5) Add Blue-Tack or any removable adhesive putty to the edge of the cups to create an airtight seal.
5) screw the cups back together
6) let them burn in/break in for 300hrs if you haven't already done so.
*The break in period is very important for these headphones. After the 300hrs the mids should open up nicely.
Clarksonius is my brother. His modded and fully burnt-in m50s sound very similar to my SRH840s when amped-they are almost indistinguishable for certain audio tracks.