[Nexus 9 Q&A, Help & Troubleshooting] JMTurbo:
Hoping someone might see this as useful......it sure has been a 12hr nightmare! This all started because my N9 LTE was AWFUL SLOW, like going from one app to the other took 20 seconds for it to do anything, hit a text box and 20-30sec for the keyboard to pop up, all not normal, my wife has a Galaxy Tab 2 and it's 100times faster so I decided I would try and install a custom ROM........... after spending 12hrs trying to install CM13 on my Nexus 9 LTE and it giving me errors upon booting to using TWRP I did a bunch of wipes and formatting, rooted the device, tried to get it back to factory ROM etc. and then I thought I might have a bricked the tablet :'( Here's my story.

After ~8hrs of trying to install stuff from the first custom ROM I tried, then CM13 and of course reading A LOT of websites and trying to install CM13 with it not working I decided to do a clean install of CM13 and follow the steps in this thread to make it work: http://xdaforums.com/nexus-9/orig-development/rom-cyanogenmod-13-nexus-9-lte-t3273566

Installation instructions

-Check if you have the latest bootloader (3.48.0.0135) and updated /vendor partition from the latest image OR just flash latest image (MMB29K) (it says here MMB29k but latest is MMV29V so I used that)

-Flash a custom recovery

-Factory Reset

-Install ROM

-Install GApps

First Step was Flashing the Latest factory Image. I went to this Website: https://developers.google.com/android/nexus/images#volantisg

Downloaded the MMB29V, used 7Zip to get to the proper folder/files.

Used this Method here to flash to factory: http://www.droidviews.com/restore-nexus-9-stock-using-factory-images/

I was able to get this to work:

fastboot flash bootloader bootloader-flounder-3.43.0.0XXX.img

fastboot reboot-bootloader

Then I tried this:

fastboot –w update image-volantis-mmb29v.zip

However I get an error saying:

target reported max download size of 518205818 bytes
archive does not contain 'boot.sig'
archive does not contain 'recovery.sig'
failed to allocate -1985890160 bytes
error: update package missing system.img

I then tried to install these files manually and the system.img always fails.

After trying that several times trying to wipe then re-install etc. it didn't work and it was midnight and I was getting a little panicked, then I come across this thread: http://xdaforums.com/nexus-9/help/marshmallow-ota-update-bricked-nexus-9-t3334871 and I thought WOW, thank god a solution and I'll get to have Android N, kinda cool.

I download the proper OTA file from here for my LTE model: https://developer.android.com/preview/download-ota.html

file: volantisg-ota-NPC56X-2-2edd174f.zip

I installed this file in the ADB/Fastboot folder then per the directions on my Tablet I went to recovery and, Wiped Cache chose “Apply Update from ADB”.

I then opened the command prompt, checked the device was connected using "ADB Devices", confirmed it’s there so then I tried: "adb sideload volantisg-ota-npc56x-2-2edd174f.zip"

It started working, got to ~35% then I get:

Total xfer:1.00x

on the command prompt window

and also

This Package is for "Flounder_LTE" devices; this is a "flounder"
E:Error in /sideload/package.zip
(Status 7)
Installation Aborted

on the tablet

So I thought that was weird since I clearly have an LTE device so I decided to download and try the regular N9 OTA image file: volantis-ota-NPC56X-2-3fa71d1a.zip

I then opened the command prompt, checked the device was connected using "ADB Devices", confirmed it’s there so then I tried: "adb sideload volantis-ota-npc56x-2-3fa71d1a.zip"

It WORKED!!! Felt like at least something was successful after 12hrs of screwing around with this.

Booted up everything was good went into the setup and all is good.....EXCEPT now I don't have LTE :'( my N9 is at 2% battery life so I will let it charge overnight and tomorrow and try and figure out how I can do this over again............if someone has thoughts or suggestion on something I did wrong in order to get CM13 in here I'm all ears.

Thanks!