I cannot get a single hid dumper to work on windows linux etc multiple boxes, different errors etc. It's such a pain.
I'm 99% sure that it's 16bit xy's but I can't verify. It's annoying because most gamepad hid examples are 8bit. I have a sniffer working and I'm sure I could modify it to dump the hids, but I can't even walk before I run here.
Yes, the xbox360 controller uses 16 bits for joysticks.