Mario Kart GP works fine with non-wavebird GC controller on r125.Yes, the "Reset" combo is (R + Z + B + D-Pad Down) on the GC controller, I don't think there is one for system "Shutdown".
I can confirm the Mario Kart Arcade GP does NOT work with game GC controller (Wii/r125/WaveBird).
But, CustomRobo [GXCE01] 1:1 works fine in r125 now.
Edit1: All Donkey Kongas & Jungle Beat seem to be working in r125, however, the DK Bongo controller does NOT. Mix values maybe?