I'm thinking a lot of folks are confusing dual temperature displays with dual input unit's which apparently exist but at a much higher price range than the one's the majority of bullet casters use. One of the stickies is about a dual setup to control a lead pot and some other separate piece of gear. He used the Auber SLY-2352 controller. That would be 2@ of both the PID and the TC's. A separate input (TC) for each controller and controlling 2 different apparatus'. Within a matter of seconds the temperature in a casting pots lead is going to be about the same throughout the mix/alloy. Lead conducts heat very rapidly. I've had a probe in 1/2" off the bottom and another 1/2" below the top and the difference between the 2 is negligible if any.
You just aren't going to have a pot of lead at 2 different temperatures and regulate our pots that only plug into one power source. Just can't happen.