Long title! I just purchased an amp that has balanced dual 3pin XLR headphone outputs, and you guessed it, I don't have a cable for it. I do have the stock ZMF cable with the balanced 4 pin XLR termination.
So, two solutions to this:
1) Dual 3 pin XLR male to 4 pin XLR female adapter. Checking Amazon and Ebay, there are a couple of nice looking silver ones that would ship from China that look like they'd work, but I'd love to buy from a head-fier if at all possible.
2) ZMF/Audeze cable with dual 3 pin XLR termination. Let me know if you have one of these lying around from an old LCD-2 or something