I also encountered

Cache formatting was not succesful, flashing may fail, check your partitions on deviceFailed to enter Recovery

with the old instructions. With the new instructions with the installer, the installer is stuck at Flashing firmware forever.
I am not sure if I followed the instructions correctly.

Even though the output looks correct, the OS looks the same after booting, not like AOSP:

[root@localhost platform-tools]# ./fastboot flash oem ./SW_binaries_for_Xperia_AOSP_N_MR1_5.7_r1_v08_loire.img
Sending 'oem' (220783 KB)                          OKAY [  6.926s]
Writing 'oem'                                      OKAY [  3.553s]
Finished. Total time: 10.536s

It says Make sure to upgrade your device to the latest stock Android 8.0 before continuing. The Xperia X does not support Android 8, does it? Does it matter which service I choose in the Emma flash tool?