By that I take it you mean an ATB diff; its what I've got fitted in my Focus estate. Changing the FD of the MT285 is really only feasable with a complete cluster change as it involves both layshafts and some machining of the cases.

With a narrow torque band NA engine the 6 speeds are used, but I find with a road turbo engine the torque band is wide enough to only need 5 speeds.

However, I'll admit the actual gearchange of the MT285 is a lot slicker/quicker than the double syncro of the MTX.

Martin