The max current output is not stated but voltage ouput is and the voltage output is adjustable in the mode.txt file. The max voltage output that it can supply is supposedly the same as the max voltage ouput of your battery pack. The minimum might be as low as .001 volts. Not sure on that one but I'm pretty sure that it can at least go as low as 1.5V. as the manual states it can use 1.5V vibration motors.
NOTE: The negative pad is what regulates voltage and the positive pad is always "live" even when the board is off.
The current flowing in an LED is an exponential function of voltage across the LED. You don't need to know how much current is being put out by the vibration motor pads, only how much it will allow to be put out without harming the soundboard.
Using Ohm's law, you only need to know two of three variables to calculate the third. Those variables being voltage, current and resistance. If you supply the "correct" voltage to the device, and the "correct" resistance, it should only allow it to draw the "correct" current. This means that you will need a resistor, even when supplying the LED's rated voltage. When supplying the LEDs rated voltage, you would need a 1 Ohm resistor.
Some devices that provide electricity can only allow so much current through them so it is possible that the vibration motors on the pad will not allow enough current for the LEDs to light up at their standard operating efficiency. This means that you can run an LED off of it with the correct voltage and with the correct resistor but still may not get the required current. In that situation, the board's circuitry for the vibration motor pads is limiting the current flow.
I have not yet tested whether or not the vibration motor pads are putting out the correct current for the LED I am using. Also, if the correct current can be drawn off of the vibration motor pads, is that current too much for the circuitry on the soundboard to handle long term? Only Jim can answer that one. I emailed him asking if it can handle 700ma. Here's hoping he gets back to me soon and let's me know.
Edit: Did some research on LEDs and resistance and corrected a lot of wrong info. Sorry about that.