I've been so upset that I can't go S-OFF with Firewater.
As for Sunshine method, in-app payment declined my credit cards (Myanmar).
And even with my Fav custom ROM, due to base OS difference, there were problems with boot time, boot logo, ...
Finally I found this site
These are what I did.
Stock Nandroid backup and Stock recoveries downloaded from this thread
1. I firstly restored to 1.60.708.2 by restoring Stock Nandroid from that thread via TWRP recovery.
2. Restored to Stock recovery from that thread.
3. Relocked the bootloader.
4. Download this and rename to HBOOT.zip
Download this and rename to 0P6BIMG.zip
5. Enter RUU mode by the command:
fastboot oem rebootRUU
Then flash HBOOT by
fastboot flash zip HBOOT.zip
6. Then, transfer the downloaded 0P6BIMG.zip to the root of mSD via Card Reader, then insert to the phone.
7. Reboot to bootloader by
ROM flashing will start automatically.
It will take a long time to complete.
Then ur phone will boot up with 1.54.708.5 downgraded OS.
8. Then Unlock Bootloader.
9. Flash TWRP recovery.
10. Root with SU zip in TWRP.
11. Finally, use Firewater to get S-OFF.
DO IT WITH YOUR OWN RESPONSIBILITY
I've tried this method and now with SuperCID