Re-run the hack, also read the manual
When running the hack on a music keg, whilst the hack is running what you've described is EXACTLY what should be happening. If you leave the box long enough you'll notice that it reboots. Oh wait, it did. Your HU said 'EJECT', which means the box rebooted.
When it does this, simply switch the HU back to the Kenwood Keg.
I recently helped someone hack a 710, and noticed that the box rebooted 3 times. After the 3rd time I got the 'Hack complete' message. It may take more reboots.
If things still don't seem to be taking, disconnect the box from the Head Unit, wait for a minute or two, reconnect and repeat the process.