I will go out on a limb here and say they are a Hosiden manufactured item.
The DH prefix plus the overall design to me is Hosiden , who were an OEM for folks since way back and still make things, one under their name Satolex ( Satolex "Plum" is a gorgeous headphone by the way ).
If this is the case I am guessing the driver there has a strange amount of holes in it, which might be different than the typical SFI type hole arrangement.
I can't see that in the images, but can you get a closer look at the hole pattern on the driver magnets ( under the fabric dustcover )
Maybe draw a picture or describe them and/or number of holes?
This is a really neat discovery thanks so much for posting this up!
So cool.
* the plastic grille in front of the drivers on the earside may be making them sound less than ideal, but ideal is a personal thing obviously.
If there is a way to nondestructively remove that baffle to try them so nothing is in the way of the driver and your ears it might be worth a shot. IF you don't like the sound now. But it is rare and almost a one-ff so might be a crime to ruin them as they are!