Just had the opportunity to test M2 with an xbox controller and I do indeed have rumble working. (In Daytona USA anyway).
XInput=1
EnableFF=1
It was fairly weak at first.
In the service menu of the game under DRIVE BD TEST, crank "roll left" and "roll right" up high and the rumble motors will shake full strength.
I didn't mess with the ffb settings in the ini file.
Here is what I have for those, but I don't recall if these are the default or the settings I had for my MOMO wheel:
;FORCE EFFECTS PARAMETERS
;FE_CENTERING Effect (Spring centering effect)
FE_CENTERING_Gain=0.5 ;Global gain
FE_CENTERING_Coefficient=10000 ;0-10000
FE_CENTERING_Saturation=10000 ;0-10000
FE_CENTERING_Deadband=1000 ;10%
;FE_CLUTCH Effect (Friction, wheel turn hardness)
FE_CLUTCH_Gain=1.0 ;Global gain
FE_CLUTCH_Coefficient=10000 ;0-10000
;FE_LEFT,FE_RIGHT (Constant force in a direction)
FE_LEFT_Gain=1.0 ;Global gain
FE_LEFT_Magnitude=10000 ;0-10000
FE_RIGHT_Gain=1.0 ;Global gain
FE_RIGHT_Magnitude=10000 ;0-10000
;FE_UNCENTERING (Sine force, wave the wheel, rumble)
FE_UNCENTERING_Gain=1.0 ;Global gain
FE_UNCENTERING_Magnitude=10000 ;0-10000
FE_UNCENTERING_Offset=-200
FE_UNCENTERING_Phase=0
FE_UNCENTERING_Period=56000
This was with version 1.0.