I rebooted my 2011 Mac mini into its Mt Lion partition (10.8.5) and used Seas0npass 0.9.8, but I then got a “failed to reset USB counters” error message.
Research indicated that the fix for this problem is to go to Seas0npass preferences and uncheck “Quit iTunes before restore” and now I have untethered JB’d both of my ATV 2nd generations on iOS 5.3
I had reverted back to iOS 5.3 using this procedure:
I have not yet tried to JB tethered on 6.2.1
BTW: it took me 3 or 4 tries to get into DFU mode, with the power cable inserted at that point, to get it into DFU mode.