A&K says:
For MAC users, the free software - Android File Transfer is still the primary solution that we commonly recommend to AK users.
Meanwhile, we understand there are several other options available in the market place, such as: here. With that been said, through our collective experience from working with customers, each different software product still posts a different strength and weakness, as there hasn't been a perfect solution yet for Android x iOS.
To further answer your question:
Has there been some change in A&K firmware that might affect the syntax or format of playlists on your DAPs?
The playlist feature for the Astell&Kern media unit remains the same, as the playlist will need to be created anew within the media player. it can't be created from a 3rd party software or outside of the AK media unit.
Is there a Windows music program that definitely would sync playlists as well as music?
If you are connecting the SP1000 media unit with a Windows computer, you are able to drag&drop media files directly into the DAP. No 3erd patty software or driver required. SP1000 is not able to support the playlist file created from a 3rd party software or outside of the AK media unit.
Why cant I edit or write a playlist in a text editor Windows or Mac that the SP1000 will accept when transferred to it? I have tried this as a workaround, but the player treats them as blank, too.
In plain sight, the Playlist file is merely a textual content that offers the order sequence for the media unit to conduct music playback. However, each playlist file specifies the exact location of each music file that you've tagged, while the media files can be stored and scatted in either internal and external memories.
The index function (or the locations code) is the essence of why SP1000 is not able to support playlist files created anew or edited from a 3rd party software outside of the AK media unit, as the location of the files isn't identical from the computer to SP1000.
We hope the information outlined above is able to offer additional product insights for your reference.