Oh one thing I forgot to mention...I measured the current into one driver (using both an ammeter and a shunt resistor) and when idle it's about 0.3 amps. It goes up a bit when the motors running, but either way that seems a bit low to me? I've got the driver set to 4.09A peak, I take it this is correct for these motors in bipolar parallel? The motor is only a little warm, nowhere near 80°C.

I'm currently using a 225VA toroid for just the one motor. There's no perceivable temperature rise on it so maybe I can run more than one motor from this transformer?