My guess Russ would be to have one pump and one varistream, I'll check out the spec on the varistream tomorrow. but you may burn out the Transistor thats in it, if it was meant to run two pumps it would have had a bigger heat sink built into it, this helps reduce the heat from the Transistor
If you have two pumps on one varistream you would not have the flexability and both pumps would go up and down when you operate the dial, not wise if one needs more water than the other.