After reading countless threads on this subject, I've learned 3 things:
1.) The stock steel cable on the HD25-1 II is made for durability, not for sound quality.
2.) The OFC Cable from the Sennheiser HD25-13 is a great upgrade, (Sennheiser part Number 74532) Most people shorten this cable & installl a 3.5mm phone plug.
3.) This cable isn't sold in the US & must be ordered overseas.
(There are lots of cable options - including going stock HD650 cable, etc. For my purposes, I wish to keep the single sided configuration, which narrows the choices down.)
Here's a cable available from B&H:
Sennheiser part number 523875 - copper cable. Isn't this the same thing as the 74532, but perhaps with a different US part number?
Here's the same cable, listed as copper, same part number, pictured terminated with 3.5 mm plug, from a US supplier:
I've purchased a HD25-1 IIC coiled cable from Juno Records UK. I believe it's copper. It's a great upgrade, however, I really don't like the weight of it. While I'm not opposed to ordering overseas again, if B&H has what I'm looking for it just makes more sense to order from a US Supplier - especially since there will be added cost in shortening and re-terminating the cable (I'm not a DIYer).
So - 74532=523875?