Well probably me just being thick too. I am a noob to Most Things Apple so maybe just got lucky. And maybe it all stops after the first tethered JB reboot: time will tell. (Edit: just had to “boot tethered”, it worked. Hooray.)
My experience is this worked, even after i updated the ATV2 (when it told me there was an Update available, and after several failed JB attempts figured “why not”) and then Settings > General > About showed AppleTV Software = 6.0.2. After several more tries-- including a new microUSB and several half-completed upgrades using Seas0nPass “Create IPSW” option-- it showed the FireCore logo in place of Settings, and then the aTV Flash(black)v.2.3 is installed. Since then have installed & used XBMC to stream, installed Couch Surfer Pro & last.fm even having to ssh in to issue ‘dpkg…’ command.
now under Settings > General > About, the AppleTV Software = 5.3(6105). **This is after successful JB & aTV Flash applied as mentioned above, when it first said 6.0.2.
I have no dog in this fight, just want to share my experience (and extreme happiness!) in case it helps.
**Can attach SP log if interested: either the whole thing including all failures over past 48 hrs, or just a tail with the final successful install.
As always: YMMV, no promises implied, & hope it helps.
Good luck out there.