I am s-on can I still flash firmware? If so I am on ATT US which one would I use. This is all confusing to me.
with S-On you can only flash signed firmware, with same or higher version as yours, and correct CID and MID
you'll also need to relock bootloader to be able to flash it (with S-On), then unlock again.
remember signed firmware will include boot.img (kernel), and recovery.img (stock recovery), so after flashing firmware, you need to unlock again and reflash custom recovery, and whatever kernel comes with the ROM you're using.