XBox wired controller works well with mac as well thanks to the open source driver (http://tattiebogle.net/index.php/ProjectRoot/Xbox360Controll...).
I have never faced any issue using the controller to play steam games on my mac.
I have never faced any issue using the controller to play steam games on my mac.
When Mountain Lion came out I had to update the driver, which had undergone some 32bit -> 64bit change but also added in some other garbage about Xbox chat pads that was breaking when I tried to use it with my Logitech game pad. I don't remember if it kernel panicked or just didn't work. Certainly I caused a kernel panic or two while tinkering with the driver. But I got it working again, mostly by commenting out stuff I didn't want.
Or you could try to debug the source if you're up for that. I would try but don't have the expertise to help without seeing it and tinkering with it.
Restart your machine, Terminate Android File Transfer and try plugging the controller again.