Thanks for all the nice comments on the Senn wooden cups. My friend did put a lot of hours in research and finally producing them, one pair at a time. So far he has made 5 pairs and he told me he may want to stop producing them as it takes a lot of time and patience just to get a pair done. They are made from old teak from Vietnam.
Not sure if he got the idea from the PX-100...will ask him.
The cups are screwed in, by the way, providing a stronger and stable housing for the HD650 compared to the stock grills.
Sonically they give a darker background, with very, very low floor noise. Bass goes deeper and tighter and the mids and highs, smooth and sweet.