> I tried using the Plex app, hoping it would replace the HTPC that I finally junked and replaced with a TiVo. Sadly, my NAS is not powerful enough to transcode, so I'm back at square one
Instead of running something on the computer or NAS to transcode, you could try using the free VLC app on the Apple TV to access your NAS (although it currently doesn't support AC3 audio and will in a later release). You could also buy the Infuse Pro app on the store, which plays all video and audio formats (including licensed ones) from any available network share. In both these cases, the decoding/transcoding happens on the Apple TV.
Instead of running something on the computer or NAS to transcode, you could try using the free VLC app on the Apple TV to access your NAS (although it currently doesn't support AC3 audio and will in a later release). You could also buy the Infuse Pro app on the store, which plays all video and audio formats (including licensed ones) from any available network share. In both these cases, the decoding/transcoding happens on the Apple TV.