Carl, if I was to look for that cable, what would I ask for. Pardon my ignorance, I got a Stax 3030 system recently and I've already upgraded the 'phones to an Omega II (still agonising over what new energiser to get). I haven't connected it up to my Philips Dolby Headphone unit yet.
I won't give you recommendations on which cable, as matters of cabling tend to be touchy matters with audiophiles... just use a cable you like and good quality plugs. You can't really get good quality adaptor cables off the shelf (breakout cables are invariably hideous), so it would probably have to be a custom affair. Maybe you'll luck out and know someone who makes cables, I don't know.
The SRM-313 can't drive an Omega II if its life depended on it, so try and decide on an amp quickly. It's a much, much better headphone when it's not underamped.