Ok I am pretty green at jailbreaking. I successfully had a ATV at 5.0.2 and upgrading to 6.0 by accident spent weeks trying to learn more about jailbreaking and how to downgrade, what shsh blobs are and importance of backups. I tried many times to find a firmware that I could use the Plex Client and have XBMC ATV.
I got alot of run around answers and “sorry but your out of luck” responses.
What I learned from my experience:
If you have a jailbroken ATV and install ATV flash Black it automatically saves your signatures to cloud for any firmware you have installed.
I only see a reason for tiny umrella to save shsh blobs on your local hard drive on your cpu. I could not get it to work until I plug the power cord in first then the usb.
To downgrade simply run seas0npass, right clicking and select the firmware you have blobs for, let it run like usual. This is where I screwed up plug in the power cord and do the DFU mode.
Mine got stuck on finding the ipsw. Do not use the one seas0npass down loads at that time if its a old version APPLE is not signing anymore like 5.0.2, find the backed up ipsw should be in your ses0npass folder on your hard drive.
Then after 10 mins it should work.
I sucessfully went from 5.0.2 to 6.0 to 5.2 and back to 5.0.2 never backing anything up manually.
Hope this helps others