Connect your DX100 to the machine and start up MediaMonkey. You wanna configure the settings in MediaMonkey first. Configure both internal and external storage. It may take a little while to scan if you got a crap load of music like I do.
Click on the "ibasso DX100 Internal" listed on the left hand side of MediaMonkey. Select "Options." Under "Destination" copy and paste: \Music\<Playlist>\<Filename> under "Sync Music files." I also did the same thing under "Classical music files" just in case.
If you are syncing FLAC files I recommend you set up a custom preset under "Auto conversion". Its also listed in the Options tab I had mentioned earlier. Under <Add Auto-Conversion Rule...> You'll find a list of options. Next to "When the format is:" Change it to "FLAC." Now under "If any of the following conditions are true:", "For Audio bitrate" change it to "Above" and change "input" to "128 kbps." Further below change "To the following format:" to "FLAC." Customize the compressions if you wish. I recommend 6 at the most. So that would be the third to the last line then select OK.
Now under "auto sync" select the playlists that you imported. If you haven't added the playlists you can manually do it from "File/Add /Rescan Folders" and point it to where you have your playlists stored. It will add them to "Imported playlists" in MediaMonkey. Whichever playlists you select will sync once you press the auto sync button. Just check-mark the desired playlists you want to be synced and apply. Then hit the Auto-Sync button. That should be it. Happy listening.
Once you have synced everything try and have a look at both your playlists and music folder on your DX100. You'll notice they are all named the same thing. This makes it very easy to edit and add onto your DX100 and keep everything organized. When you want to add on you just update the playlist in MediaMonkey and apply the changes to the playlist (overwrite it). At which point I recommend you clear the playlists from MediaMonkey library and rescan them. This should take about 10 secs to do and will reflect the changes you made. If you intend to not add a lot you can just copy and past the new music over to the intended folder and then delete the old playlist from your DX100 and copy the updated playlist over to the DX100 Playlist folder (should be the same playlist but with the new music you added to it as well). Once you disconnect your DX100 it will reflect the same playlists but with your new music files added and in the order you put them in. Happy listening.