Hi Larry
The volume pedal sockets have a send and return in order to detect the level the pedal it set to. This sends an audio level tone out to the pedal and then measures its level when it returns, so you can use anthing that is a genuine volume pedal. The 'send' is also wired to use the ring as a return, so you can also use the Yamaha FC3 sprung continuous pedal (which Yamaha use as a sustain with their high end digital pianos) which is wired with the send/return on the tip/ring. It detects this automatically when you plug one in The signals are a/c coupled so you should be able to use almost any kind of volume pedal, impedence is not an issue.
The two switch inputs use a 5V DC sense signal and should not be connected to anything active, just noraml passive make/break style pedals, either latching or momentary according to your needs. If you connect them to anything that sources a voltage, you may damage them so don't do this.
The continuous control pedals do get used as a variable damper input for the Factory Piano, you should find this quite effective as it is a genuinely variable dampling, like an acoustic piano.
What pedals are you using?
John