After clearing the whole file system and reloading from scratch, including the playlists, it's now working correctly. I think that the previous time, I had loaded everything through Explorer, direct onto the card. I may have copied the playlists the same way. That may have affected Poweramp's ability to read the playlist files, if the filepaths weren't correct. It did seem to correctly pull up what the songs were, and clicking any individual one pulled up the right song, but it may not have then been able to find the next and through the playlist was over. This time, I synced everything painstakingly using Winamp, including the playlists once the whole file system was loaded. This imported the playlists, still as m3us, but now with the correct filepath. Now they do play through a playlist correctly. I had to do it a certain way through Winamp, however - initially it wanted to create PLA files on the SD card, but I don't think these were working right. Dragging and dropping them a different way produced m3u files on the SD card, which show up separately in Poweramp but work great.