Thanks for the clarification.

I managed to get it working by combining a 3.5mm to 6.5mm adapter with 6.5mm to 3.5mm adapter.

See sample images at: http://www.cable-trader.co.uk/images...%20adapter.jpg
and
http://www.cable-trader.co.uk/images..._5_mm_plug.JPG

Those 3.5mm splitter/adapters won't work because the male jack of the headphone is too long.

Looks clunky but it works for the moment. I'll call Beyerdynamic to ask if they could do something about it.
If someone comes across a nicer adapter please post here.

THX