i just dug up an oem 3.5mm cable that came with a computer monitor and it worked fine. using a Blueant speaker to test.
what do you mean by the HTC does not recognize the aux cable? do you not get ANY sound at all?
what speaker dock are you using? can you try another peripheral or plug it into a laptop or computer aux in?
also make sure you dont have a case on , as this could prevent the plug from going in all the way.
also, if there is a lot of material around the base of the plug you are using, this too can cause issues...