Hi. I think I know what might be happening. This is how I use J River to generate the various playlists I might need. It seems long winded but once you get going it's really quick and easy.
1. Put Poly on the same WiFi network as the computer running J River
2. Make sure DLNA is enabled and running in J River ( Tools - Options - Media Network - Enable DLNA )
3. Once DLNA is running in J River you can then see Poly as a server under the Playing Now - Playing From tabs.
4. Select Poly Server as your audio source ( This assumes your SD card is in Poly and loaded with music )
5. Select the Audio tab in J River - it should ask you to load the music library.
6. Check in the audio tab you can see all your music.
7. Now go to the Playlist tab in J River and either create your own new playlist by dragging and dropping music into a playlist folder or there is a neat thing called smartlists which will create playlists based on various options eg. Audio-all ( for all your msuic ), Audio-high bitrate ect..
8. Once the playlist has been created right click and choose export playlist and choose simple m3u. The playlist will be saved locally on your computer so select a drive or path where you can find it again.
9. Now remove the SD card from Poly, put it in your computer and copy the playlist file you exported in 8 above into the root directory of your SD card.
10. Put the SD card back into Poly and let it rebuild the database
11. Now you should be good to go with the Quickplay function.
There are of course other programs and ways to create playlists but J River has some quite powerful options and will also work on both Mac and PC.
I hope this helps.
Just a few screen grabs as well to help....