I replaced a set of chinese ebay o2 sensors on my z32 a few weeks ago and they where the exact same ones AMS sells. I am pretty sure the generic crap AMS sells (brake pads, rotors, ball joints, o2 sensors...etc) are bought from a chinese ebay supplier and then sent somewhere to have the logo's etched on and put in an AMS box.
Now I'm just waiting for someone to buy a set of control arms or a brake kit from AMS and have it fail and have it kill the driver or total the car and watch as AMS slowly backs out of the market and changes their name.