Windows DInput support 10 or 12 axes, but the axes above # 8 are reserved for POV HAT - Saitek X-52 use some of this extra axis in extra POV HAT on throttle, hence need a specific firmware with support for this axes.

An previous MMjoy2 Firmware has support for 2 POV HAT.

Then, the practical use in most games still 8 axes - don't know about X-Plane.