It seems like a silly question in hindsight, but if I had noticed that when I tried syncing with Windows Media Player, it was converting everything to WMAs, so I thought maybe the knew something I didn’t. And the WMAs were mostly readable by the Clip Zip, although the conversion process took forever, and WMP couldn’t seem remember what files it had synced previously, so on future syncs it would create a conversion of each file all over again before realizing the file was already on the device. (Just one of several inefficiencies of WMP.)
But, since my Zip was able to at least process all the WMAs without freezing, I thought maybe the Zip was just having trouble with certain formats, even though the Zip is supposed to be compatible with those formats. I figured if I was going to have my computer spend the hours needed to do all that converting, I should try to make sure I used the best format on the first try.
I ended up having Media Monkey convert all the M4As to MP3s, and the Zip was finally able to process it all. The only non-MP3 files now are some Rhapsody WMAs that use DRM.