[Kindle Fire HDX 7" & 8.9" General] fabische:
Eureka!

I have LineageOS 14.1 (Nougat) running on my Apollo!

Thanks a lot to davey126, draxie, ggow, Hashcode, Onyx, Shoog03 & the usual suspects for their excellent support!!!

To all of you who were like me somewhat confused by the procedures described in this thread, here is a step-by-step guide of how I have unlocked the bootloader and installed LineageOS.

Apollo users can download all the required files mentioned in the following paragraphs here in one single zip file:

https://drive.google.com/file/d/0BzWXs0Pv6tCRSDdocWNuRkN6cFE/view?usp=sharing

Before you begin, make sure and check with Root Checker and supersu that your device is 100% rooted. Also, make sure that you have activated ADB debugging options in developer options.

Tutorial: HOW TO UPDATE KINDLE FIRE HDX TO ANDROID 7.1 (Nougat)

PREPARATIONS TO UNLOCK THE BOOTLOADER (ADB DRIVERS & UNLOCK SCRIPTS)

I have used a Windows computer. First you'll need ADB/FASTBOOT for Windows:

1.a Download & extract minimal_adb_fastboot_v1.4.2_setup to c:\ADB

(direct download https://www.androidfilehost.com/?fid=745425885120698566 from this thread https://xdaforums.com/showthread.php?t=2317790 )

1.b Download and install HDX drivers from Amazon:

https://s3.amazonaws.com/android-sdk-manager/redist/kindle_fire_usb_driver.zip

2. Download & extract "unlock.zip" INTO ADB FOLDER (!)

(direct download https://xdaforums.com/attachment.php?attachmentid=4029485&stc=1&d=1486245411

from this thread https://xdaforums.com/showpost.php?p=70881555&postcount=550 )

3. open Windows command promt right click as administrator

3.a Navigate to c:\ADB

4. Enter "adb devices" (daemon is started, connection established, confirmed by a device number)

UNLOCK PROCEDURE

5. From Windows Explorer run the batch file "get_code.bat" from your adb folder

6. The batch file will save the file "unlock.code" into the adb folder

FLASH VULNERABLE ABOOT & TWRP

Check that all these commands executed without errors. If your firmware <=13(14)3.2.3.2 skip this step.

Download aboot and twrp for Thor (Kindle Fire HDX 7)

https://drive.google.com/open?id=0B2twXJIOgv-UMGxXMUZPZTlZTUk

or for Apollo (Kindle Fire HDX 8.9) -

https://drive.google.com/open?id=0B2twXJIOgv-URzJDQkczNzRLaHM

and put this two files (twrp_cubed.img and aboot_vuln.mbn) into ROOT DIRECTORY of your kindle internal storage.

7. Establish ADB Connection (ADB devices) and enter - if you are NOT running Safestrap - to following commands:

adb shell

su

(NOTE!! MAKE SURE YOU ALLOW THE SU REQUEST ON YOUR HDX SCREEN!!!)

dd if=/sdcard/twrp_cubed.img of=/dev/block/platform/msm_sdcc.1/by-name/recovery

dd if=/sdcard/aboot_vuln.mbn of=/dev/block/platform/msm_sdcc.1/by-name/aboot

If you get "not such file or directory" after entering the above commands (SAFESTRAP related ):

SAFESTRAP USERS ENTER INSTEAD:

adb shell

su

dd if=/storage/emulated/0/twrp_cubed.img of=/dev/block/platform/msm_sdcc.1/by-name/recovery

dd if=/storage/emulated/0/aboot_vuln.mbn of=/dev/block/platform/msm_sdcc.1/by-name/aboot

It worked for me!

[IMG="Safestrap Flash"]https://abload.de/img/safestrapsolution4zyo4.jpg[/IMG]

ACTUAL UNLOCK PROCEDURE

8. From Windows Explorer run the batch file "unlock.bat" from your adb folder (HDX will enter Fastboot mode)

If everything works correct the result should look like this:

[IMG="Unlock confirmation"]https://abload.de/img/unlockok3ikkl.jpg[/IMG]

8. Finally, exit fastboot mode by pressing power & Volume Up for 20 seconds, this should initiate a reboot

IMPORTANT: in case fastmode screen remains on < waiting for any device > in the Command window

WORKAROUND

You'll need to manually select the adb driver for windows:

a) Open Windows Device Manager: Right-click Start Button and choose Device Manager. Win7: Click Start button and type Device Man [enter]

b) Find Fire under Other Devices, right-click it, and choose Update Driver Software.

c) Press Browse my computer for driver software and then "Let me pick from a list of device drivers on my computer".

Then Find Android Device, click it and press Next. Then choose "ANDROID COMPOSITE ADB INTERFACE" (!!!) in right, and press Next.

More adb connection info here: https://xdaforums.com/fire-hd/general/guide-install-windows-adb-drivers-fire-t3189000

INSTALLING LINEAGEO" (CM14.1 - NOUGAT)

XDA THREAD LineageOS (CM14.1)

https://xdaforums.com/kindle-fire-hdx/orig-development/rom-cm-14-1-thor-t3517481

First you need to

UPDATE TWRP to Nougat requirements

https://xdaforums.com/kindle-fire-hdx/development/recovery-twrp-3-0-0-0-t3322547

In my case after unlocking the bootloader my previous Android Kitkat installation had disappeared. However, TWRP was working. Hashcode writes in his first post of the LineageOS thread that TWRP needs to be updated for Nougat. I could update TWRP to Version 3.0.3.1 by activating "ADB Sideloading" in TWRP, connecting the device to my PC via ADB and the entering (in my case) "fastboot flash recovery apollo-twrp-3.0.3-1"

Then, I downloaded the latest LineageOS Release for Apollo + Google Apps for Nougat (more here: https://xdaforums.com/kindle-fire-hdx/orig-development/rom-cm-14-1-thor-t3517481 ) and installed both by using again the command "adb sideload <filename>.zip" .

Done!

After rebooting, my Apollo is running a shiny new fast and buttery smooth Andoird 7.1

[IMG="Nougat!"]https://abload.de/img/nougat2rru64.png[/IMG]