Indeed, it does seem like I was "asking for it" when I decided to go with the walled garden. Here's the latest. According to the MusicShifter customer service person:
Quote:
We probably didn't have the "Optimize M4A" step in our process back then. We've found that this fixes streaming issues with both Apple Lossless and AAC.

The solution for you is to download dBpowerAmp from www.dbpoweramp.com, and download the m4a utilities add-on package here (bottom of page):

http://www.dbpoweramp.com/codec-central-m4a.htm

Then run all of your ALAC files through this. It should fix the problem. What it does is it moves the metadata to the beginning of the file so that the device being streamed to (Apple TV) knows what it's getting and can begin playing the incoming stream.

Note that this tool only runs on Windows (XP/Vista). I don't know of a similar tool for the Mac.

Let us know if you need more help.

Sorry for the trouble!


That seems to explain what's going on. Before trying dBpowerAmp or whatever, I decided to try drakino's "reencode" idea. Success! Now I just need to start the machine doing a pass across all of its files. Back-of-the-envelope says it will be about a solid day of compute time.