Hey!
SE Firmwares are 3 files: MAIN (That's the one you got), FS and CDA. I don't recommend CID53 because you won't ber able to patch the phone for free. SETool3Box is a paid hardware component that uses a free software but requires this box to work.
Use these:
Downloads - R8BF003_RED52 - K790_R8BF003_MAIN_GENERIC_EV_RED52 - SE Users
Downloads - R8BF003_RED52 - K790_R8BF003_FS_CENT_EUROPE_RED52 - SE Users
Downloads - K790 - HB1-06_Generic_CDA102568_106_R3A_GENERIC_AMERICA_1 - SE Users
Use the CENT EUROPE FS becuase there's no AMERICA yet.
If your phone is allready CID 53 you are forced to use a CID 53 firmware, if not - use CID 52.-