The sound board drive signal is exactly the same as for solenoids. The driver board does not put out any voltage, but instead pulls the line to ground when activated. With solenoids or chimes, the other end of coil is connected to +24V. And with the 3-tone sound board, the driver just grounds the input allowing the tone generator to operate.
If you use a custom sound board, it needs to have active low inputs, and pullup resistors to 5 V or whatever is the board operating voltage.