Your jailbreaking procedures states: «Some AppleTV software versions require a tethered boot. This means the AppleTV must be connected to a computer for a brief moment during startup.»
What Apple TV software requires a tethered boot ? I have actualy the latest ATV software
That statement is obsolete. It applied before the latest SeasonPass was released that now supports an untethered boot even using the latest Apple firmware.
Sorry for the confusion. The latest tethered/un-tethered info can always be found near the top of the Seas0nPass guide.
"NOTE: Seas0nPass provides an 'un-tethered' jailbreak for the latest 4.2.1 (iOS 4.3) AppleTV software. This means the steps found under the "Using Seas0nPass for a tethered boot" section can be skipped."