You seem to be getting mixed up between the ATV Flash (Black) FireCore software that provides addtional apps and the jailbreaking software (SeasonPass)?
The FireCore ATV Flash (black) software runs on jailbroken systems - it does notcare whether the jailbreak is tethered or untethered or what tool was used to do the jailbreak. The current release requires you to be on firmware version 4.4.4 or later to get correct operation.
The jailbreaking software is Seasonpass and this allows you to select the version of firmware to be used (it defaults to 5.3 which is a tethered jailbreak0. However you can only select versions of firmware that Apple is still signing (i.e. 5.3) or for which you already have saved shsh blobs (which are version + device specific). If you already have a version of firmware that is earlier than 5.3 on your ATV, then there is an option to save the shsh blobs that correspond to that version on your device.