recabling my Stax sr-009 to pure copper cable

Since the Stax 009 cables are not interchangeable, I would refrain from changing them. To me, that's like changing the engine in a Ferrari to a high performance Chevy engine. It might go faster, might not, but what's the point? If you want a different sound, buy a different headphone (one with interchangeable cables) then experiment with different conductors all you want. The idea of cutting through the flat Stax cables and then twisting or soldering the wires to other types of cables is ridiculous. Ruin them if you want to, they're your headphones, but at least you have my opinion. 

I fully support the comment by stringreen. The Stax 009 are great phones (I know, I own them), but if you aren't happy with them, move on. There are any number of headphones available out there, surely one will be to your liking. I strongly advise against defacing the Stax phones as it will make them difficult to sell.