Had a look at my DAC, the XLR (analog line) out is male indeed and the input of my amp female.
If I look at this: http://www.littledot.net/forum/viewtopic.php?f=9&t=822
The XLR headphone out is female.
Just a convention?
I have heard the Japanese standard for XLR was reverse of US/AES standard (14). So perhaps the Japanese being dominant in headphone manufacturing in early years led to that.