I have a home-made 6-pin extension cable I'm willing to sell. Actually, it has 5 pins on the male side and 6 on the female side, so it will connect any Stax to any other Stax; it's compatible with both standard and pro bias phones and amps/adapters.
It's quite long -- more than 10 feet. I can send pictures if you're very interested.
Since interest has been expressed by more than one person, I've posted my Stax "universal" extension cable for sale on a new thread on this forum. Please look for it there, and let me know if you're interested.