Hi guys, I played around with foobar a little and may have found a slightly easier method. Only caveats are that you will need the same folder structure on your microSD card in your X3/X5 and on your computer (just the music part), and also be able to install components for foobar.
Step 1: Install the EXTM3U playlist component from here:
http://skipyrich.com/wiki/Foobar2000:EXTM3U_playlist_format_plugin
Step 2: Create playlists in foobar like as usual (manually or using the autoplaylist function) and then select the playlist you want to make a file out of. Make sure the playlist is playing (or at least, has its songs shown on the main window).
Step 3: Move your cursor to the top, you should be able to see "File". Click on it, and then click on "Save Playlist as EXTM3U".
Step 4: Rename the playlist (It will name the playlist with whatever song you have highlighted by default) as desired. Save the playlist such that it is just one folder above all your songs (foobar will create relative paths for you if you do this. It will create absolute paths if you save it at other locations.)
Example:
You have songs at the following folders (and each of them have their own subfolders):
C:\Music\Jazz
C:\Music\Rock
C:\Music\Anime
Save the playlist in here:
C:\Music
The playlist now will look like this in NotePad (In between each entry leading to the song location, there will be another line starting with # and have the metadata of the song; this is meant for EXTM3U usage. I hope the X3/X5 will be ok with that):
#EXTM3U
#[song metadata]
Jazz\AlbumA\Song1
#[song metadata]
Jazz\AlbumA\Song2
#[song metadata]
Jazz\AlbumB\Song1
#[song metadata]
Rock\AlbumA\Song1
#[song metadata]
Anime\AlbumA\Song1
Step 5: Copy the playlist over to the X3/X5 and you are done! If you want, you can use FreeFileSync to make things a little easier.
Note: You can also just use foobar to work on the files on the X3/X5 directly, but this means that you will need to drag and drop the files onto the foobar window each time you want to do all these.
Hope this works out (yes, even Japanese characters are showing up fine in Notepad in the sample playlist I made even though it is a m3u file), would love to be able to confirm that this will work on the X3/X5 right now but my paycheck issues are preventing me from getting the X5...
PS: Reposted from the playlist thread; just realised that it might be better to post here too...