hio77: My, that's really gotten confused!
I'm not quite sure what to advise as I've got more questions about why it's worked the way it has..
6.00.12 is the factory firmware currently. So your other one will have been updated.
Upgrade button will take you to the mesh firmware upgrade screen. So that won't be too useful with a second smart modem.
Currently spark doesn't provide direct links to the firmware.
If you have questions, I am more than happy to answer them!
Should I plug them both into the ONT and let them both update (individually, of course) and then revisit the config pages? How long would the take once connected? I run a different router normally that has a specific config for my network, so couldn't leave it more than an hour or two.
By the way, here's the device list, again showing the 2nd modem linked to the first with devices connected to both units: