I hope this helps from a newbie pov. If this is deemed misleading by the more experience and expert among you please let me know and I will remove it (if I can).
The process wasn’t obvious from the Seas0nPass instructions that I had to go all through the Create IPSW process. I thought that was the tethered option and avoided it. I pieced together what was going wrong from two or three entries on the forum and a little help from nakan.
First make sure you have a version of the 4.4.3 IPSW on the PC. I also had to install .net 4 and upgrade iTunes.
Select the Create IPSW option first holding down shift , even though we’re doing a tethered boot, select the 4.4.3 file that should have SP in the filename* and follow those instrcution to the letter. It will launch iTunes (which I didn’t expect) and select the automatic restore option it gives you. You’ll end the process with USB connected and power on the aTV2.
*(I had to run the process twice to create the SP version although I’m reasonably certain that it would have been created from the Internet version of 4.4.3 IPSW on the first pass)
Disconnect power and USB then run Seas0nPass again and follow the untethered boot option. Again follow instructions to the letter.
After that aTV Flash installed like a dream including running files from my Buffalo NAS, flac, mkv, mp3 etc. iPad2 connects seamlessly - it is outstandingly fabulous. (Sorry to gush so - I’m just very impressed).
Again, experts, if this is misleading or plain wrong please let me know so I can delete it.