Guys... Please read the previous pages of the thread before attempting something. All of this has been tried and has not worked.
We can't flash a new ROM because the preloader and kernel have boot, system and recovery image verification. If any of the images cannot be verified, the device does not boot! When you reflash the stock ROM, you would end up losing NVRAM data (IMEIs, WiFi MAC Address). A version of TWRP had been ported to this but it caused verification errors and didn't allow the device to go even into recovery.
If you downgrade, root and then upgrade, the image verification does not let it boot.
Remote download (fastboot flash recovery) is not allowed due to the image verification and fastboot restrictions.
The only way is to decompile the preloader and kernel files and remove the image verification from them (which is what I am working on). Only then we would be able to flash recoveries/ROMs/SuperSU as we please.
If you still want to go ahead and flash something, use the SP Flash Tool but be warned: Flashing anything root related will render the device un-bootable! Be sure to write down your IMEIs and WiFi MAC Address if you must continue.