I'm looking at this thread, and its posts / links, and I'm a bit confused. For no really good reason at all, can you clarify what you are trying to connect to what and why?
Here's what I think - and correct me if I'm wrong.
You have a source whose output is taken from a female 1/8" stereo headphone receptacle.
You want to connect that source to the input of the HP2 headphone amplifier. Its input is a male 5-pin mini-XLR receptacle.
Now that HP2 comes with a cable that allows you to connect two (2) stereo inputs to that single mini-XLR input. That cable has a female 5-pin mini-XLR connector at one end (which connects to the HP2's input) and two (2) regular size female 3-pin XLR plugs at the other end.
It seems to me that you therefore have multiple connection / connector choices besides the $35 cable shown in the OP.
Here's one way to tackle it.
You could use the provided cable and Rube Goldberg the following:
1. attach this
http://www.parts-express.com/parts-express-xlr-male-to-1-4-stereo-female-adapter--240-436 to this
2.
http://www.parts-express.com/1-4-stereo-m-to-35mm-stereo-f-adapter--091-1025 to this
3.
http://www.bestbuy.com/site/kanex-6-audio-cable-purple/5586847.p?skuId=5586847 (which you might already own).
One end attaches to your source and the other to the HP2's included two-headed cable. Voila!
Total cost $11.57 (n/incl shipping if you buy online.)
Or you could buy the $35 cable in the OP - assuming that its pin configuration properly converts the single stereo 3-pin to the dual stereo 5-pin of the HP2.
Jeff