ive never been able to get the 6th axis of any controller to be detected by the game, and ive owned a lot, 2 saiteks, ch, countless virtual joysticks, like ch/ppjoy, and even some diy sticks. it has never concerned me because the game only has like 5 bindable axes anyway, some of which are redundant (absolute/relative throttle for example). it could be a bug, like an off by one error in a loop somewhere. but ive never been able to make heads or tails of the input code.
with some scripting hacks i was able to fake 6dof flight, by adding lateral thrusters with mouse axes (and then configuring those axes as mouse axes in whatever control profile software you use), and a partitioned throttle alowing you analog control of reverse thrusters. but yea this is stuff ive waited years and years for and im still waiting. using scripts to upgrade a fundamental system in a game engine seem hackish to me.