Going off your post, I think you need to get the adapter from x-gaming.  I wouldn't mess with a DIY solution for a usb conversion.  If you really need to avoid that adapter or if there are truly "no wires," then get a xin-mo and wire it up as if it weren't an actual x-arcade.  The box itself and the controls are probably worth more than you paid and you might be able to get something for the x-arcade encoder after you pull it.