Well, we couldn't replicate the problem. But we finally got around to replace the old library that was used to handle joystick input with a more modern one, which, hopefully, also fixes this issue. More importantly for everybody, we finally killed the need to define a "preferred device" in order for Steel Beasts to accept your input. Of course, all this still needs to be tested.
So there's hope that by replacing the joystick input library this will also eliminate whatever prevented the proper recognition of your X56. If, after the next patch or upgrade (whichever materializes first) the issue persists, we'll have to look into the matter again. Until then I can but ask you to hold out.