My car will use EXTINF data to display songs if it is in the m3u file, but playlists exported from subsonic don't contain any. Otherwise the car displays the filename. Here's a sample format:
Extended M3U playlist:
#EXTM3U
#EXTINF:199,In The Flesh
R:\Music\Pink Floyd\1979---The_Wall_CD1\1.In_The_Flesh.mp3
#EXTINF:217,One Of My Turns
R:\Music\Pink Floyd\1979---The_Wall_CD1\10.One_Of_My_Turns.mp3
The number after EXTINF: is the duration of the song in seconds. After the comma is the display name of the track.
More info here: http://en.wikipedia.org/wiki/M3U.
I also have to edit out the R:\Music when I copy stuff to a sd card but it's not a big deal to search and replace that in one command.
thanks
steve