@ggilley FWIW, I've used the QNAP QSW-308-1C with the unified RJ45/SFP+. That worked, and so did the Planet Technologies XT-705A.
I've also tried the UniFi Flex XG, and that didn't work. For some reason the ATT router didn't want to passthrough or assign an IP, but I could manually assign an address on the subnet (vs passthrough).
The other thing to be mindful of, performance compared to the on-router speedtest. The HUMAX router seems to lose about 300Mbps, and then the media converters may lose a bit too.
Another FYI, unlocking x710 for any SFP+ module
https://forums.servethehome.com/index.php?threads/unlocking-any-brand-sfp-modules-on-intel-x710.29040/
unlocking x520 for any SFP+ module
https://forums.servethehome.com/index.php?threads/patching-intel-x520-eeprom-to-unlock-all-sfp-transceivers.24634/
Follow up with what kind of performance you get. I've noticed all sorts of variations with different equipment. It's hard to say what's best, even though they all sync on the AT&T side.