For those of you who had tried the above with no luck, here is a quick update about how I just unbricked my Nexus 9 device after a stock OTA update.
All of the above is correct but when I tried to sideload the latest version of the volantis.zip file I received an error message, something like
E: sigature verification failed
E: ... Aborted
The solution was surprisingly simple
Sideload the very next version that the device currently has installed wich you can find on the second line of the recovery screen, in my case this was 6.0.1 (MOB30D)
I was nearly ready to give up but am currently updating to the latest android version after going back in and enabling USB debugging and the Bootloader (which were bother disabled before) then I managed to flash to 7.0.0 (NRD90M) with no problems or errors.
Next just a manual update from the device to the latest version.