If I remember - acknex uses 12 up to 32 buttons on the joy and 4 are the dpad.
In the past to get the button numbers i believe I used a calibration app in the windows control panel.

You should be able to use a function to debug_var the joy button numbers.

Check out joy button http://www.conitec.net/beta/joy_buttons.htm
And joy_pressed in key.c