I couldn't find the solution searching here or the interwebs, so I just wanted to post this up so there's a record of it. Yesterday, I jailbroke ATV2 #1 without much problem. Tonight, I tackled ATV2 #2 and just couldn't enter DFU mode to seal the deal. I tried every trick in the book -- from different orders for plugging in the USB and power cables, to menu-down, to deleting preferences for Seas0nPass and starting over from scratch. I tried setting the ATV2 up and then jailbreaking. I tried restoring to factory default and doing it. Nothing worked. Frustrated, I flashedback to my pre-Mac days and just restarted the damned computer. LoL! Guess what? It worked! I used the default Seas0nPass instructions (just the menu-play for 7 seconds), DFU mode engaged, and the jailbreak was successful. So ... for those of you having DFU problems that don't seem to be resolved by any method available on the net, restart your Mac and try again.