I’ve posted this same issue in the more active XBMC forum and have gotten a variety of responses – including those from individuals who were stymied and had to do just as you said to be able to tether boot, while others seemed to be able to simply do the quick “tether boot” download without creating an IPSW.
Some posters said they were ALWAYS presented with the “tether boot” option after opening Seasonpass, others said they only saw a the click-able icon option once they downloaded the IPSW.
A very respected veteran poster chimed in that there would ALWAYS be a tether boot option presented – as long as the ATV was attached to the computer… implying that anyone being presented with a “grayed-out” option of the “tethered boot” recieved it because they did not have their ATV’s Micro-USB(ed) into their computer.
It really doesn’t seem like both situations should exist.
Why would some users get a “grayed-out” option, while others don’t?