I had some extra pads to play around with from my m50x - Dekoni ($40) and WickedCushions ($20), both pleather and memory foam. Neither will slot easily so I had to wrap them around the cups.
The signature with the dekonis, although better than the "stock" pads, was a bit weird. They introduced some deep notches in the highs around 8-9 kHz.
The Wicked Cushions I had modified by removing the filters altogether. Surprisingly, even though they sounded bad with the m50x, here got really close to the signature of the "new original" pads, just with slightly more bass. The added benefit is that they are really big, fat and comfy, and move the drivers away from your ears so they aren't touching, and making the sound stage wider.