Thanks tmc, that sounds like a perfect plan. I am going to unbundle the rats nest this weekend, number each wire coming out of the brown cable jackets as to what zone the current system says it is, and then go ahead and plug into the Rachio. There is a spot for a master valve, but from what I can see without unbundling the wires, it doesn’t seem to be hooked up.
Part of what sold me on Rachio is this community!