Location of Multi-zone box

[RS505]

I'm about to replace both of my old Penguin AC units with new 15K Penguin2 with HP units.

I'm also going to put a single micro-air thermostat to control everything.

I suspect that there is, located somewhere on this rig, a silver box with a couple of wires leading to the Aquahot, and an RJ-45 cable leading to the rear AC. It controls the "zone 2 furnace" zone in the old system.

I'm wondering I anyone has any good idea of where to look for this thing. So far, I've looked under bathroom sink, behind bedroom TV, behind dryer.

Thanks in advance for any pointers