Obtain these files:
s53200ce9.15.6-step-upgrade.pkgcmterm-s53200ce10_11_2_2.k3.cop.sgn
Apply these in order, this will bring your device to RoomOS 10.11.2.
From here, register with a free WebEx account, let the device download the latest RoomOS 11.x build, it will automatically reboot. You can upload the files through the web interface -> software
Hint: To keep admin/other accounts active: xCommand Webex Registration Start SecurityAction: NoAction ActivationCode: "123456"
TODO: investigate https://$ROOKIT_IP/web/logs/file/current/eventlog/softwareupgrade.log to get unauthenticated pkg files