hi. the maximum voltage is 1.8 via the system bios. check the regulators specifications, only says 1.8 Volts.
some rumors say they can have theirs as high as 1.825, 1.85 and 1.875 after vid pinning. methinks its not true. its just probably voltage fluctuations.
there is also a rumor of the old bios version 1010 as capable of having above 2 volts via the bios. i think it is not true also. i think asus made a mistake about it as it is physically impossible to make a voltage regulator whose maximum capacity is 1.8 volts to suddenly become above 2 volts with just a BIOS update. you need to physically reconfigure the chip for this to be possible.
i regret buying this motherboard because of its low voltage via bios. had good reviews about it as the best overclocker of the p3 tualatin, but now methinks those review sites are lame.