I figured it out. For anyone trying to get an RTH6580WF to work, you can configure it as a “Honeywell 9000 Wifi Thermostat”. Here’s how:
In the app, under the “My Home” tab, click the + (Add a Thing).
Click “Add Device Manually”.
Click "Thermostats"
Select “Honeywell Wi-Fi 9000 Thermostat”.
Connect Now
Follow the steps entering your credentials and selecting the thermostats (it supports multiple) that are already configured under the Total Comfort Connect config.