SUCCESS!!! It didn't work last night but this morning I tried again and it's exactly as you suggested. I reformatted the sd card a couple times, plug the dx90 into my computer, then I created a new folder in the sd card, I named the folder whatever the name of the playlist will be, and then I drag the entire contents of the the playlist over to that folder. Simple. And then I repeat for the next playlist....and so on and so on. Maybe the problem was with the sd card. I used the same one I've been using in my phone (128GB) and a couple times in the past I've removed it from my phone while forgetting to "unmount" it. Maybe I did something to the card. In any case, I woke up this morning thinking about you saying that this is what YOU do with your playlists and I thought that if it works for you it should work for me so I tried again. I still think the ibasso playlist system is wrong, but this suggestion of yours does a run-around the ibasso playlist system and still preserves all the functionality of a playlist. Thank you so much.
I was getting ready to send it back. Without your response to my pleas, I definitely would have given up which would have been a real shame because this thing sounds very very nice. Hard to believe a portable can sound so good. Much better than the Fiio x3(original).