I don’t know why the 1M resister unless they want to limit current flow in the control circuit. Hard to get much current to flow across a 1M load. I think I would put it in the circuit if CR Magnetics recommends it, assuming the EZIO8SA input works with it. I looked through the CR Magnetics web site but could not find a device with the model number you listed. With the opto-isolated Input working with 4.5 and not with 2.5, it suggests the 3-30 VDC value in the quick-start guide was the correct one. The 4.5 value sounds like a reliable value to control either the opto-isolated or digital Input. I’ve had good results with the Simplehomenet devices I use. Don’t have an EZIO8SA, but the Inputs on 3 EZIO2X4s, 1 EZIO6I, and an old EZIO8T (which I no longer use) have worked well. Glad your up and running.