I might have some more help, as I just got my FiiO X5 and found some interesting quirks that are quite straight forward when dealing with a device that has multiple storage mount points. So here are two examples of .M3U8 files I'm using, but one is created by MC and the other is a modified one based off of the MC. When using .M3U8, you may get better (or real) Unicode support, but I didn't see absolute paths. This is normally fine when working with a single mount, but multiple sources are problematic.
Original "Run the Trap" playlist created by MC for the X5 using the first microSDXC card slot (TF1):
\Music\Eliminate\Hyper EP\01 - Eastern Swing (Original Mix).mp3
\Music\Flux Pavilion\All Trap Music 2 [Explicit]\26 - Do or Die (Flosstradamus Remix) [Explicit].mp3
\Music\RL Grime\All Trap Music 2 [Explicit]\33 - Shells [Explicit].mp3
\Music\Apashe\Battle Royale_Black Gold (VIP and Remixes)\01 - Battle Royale (Feat. Panther) (VIP).mp3
\Music\Apashe\Battle Royale_Black Gold (VIP and Remixes)\02 - Battle Royale (Feat. Panther) (Tha Trickaz Remix).mp3
\Music\Apashe\Black Mythology\01 - Black Gold.mp3
\Music\Apashe, Dabin, Kai Wachi\Black Mythology\02 - Forsaken.mp3
\Music\Mantis\Block Rocka\01 - Block Rocka.mp3
\Music\Kai Wachi\Echelon\01 - Echelon (Original Mix).mp3
\Music\Aero Chord\EDM.com Exclusive\01 - Bouzouki [EDM.com Excluisve].mp3
\Music\Aryay\EDM.com Free Downloads\01 - The Lawnmower by Aryay.mp3
Original "Run the Trap" playlist created by MC for the X5 using the first microSDXC card slot (TF1), and then modified to work:
#EXTM3U
TF1:\Music\Eliminate\Hyper EP\01 - Eastern Swing (Original Mix).mp3
TF1:\Music\Flux Pavilion\All Trap Music 2 [Explicit]\26 - Do or Die (Flosstradamus Remix) [Explicit].mp3
TF1:\Music\RL Grime\All Trap Music 2 [Explicit]\33 - Shells [Explicit].mp3
TF1:\Music\Apashe\Battle Royale_Black Gold (VIP and Remixes)\01 - Battle Royale (Feat. Panther) (VIP).mp3
TF1:\Music\Apashe\Battle Royale_Black Gold (VIP and Remixes)\02 - Battle Royale (Feat. Panther) (Tha Trickaz Remix).mp3
TF1:\Music\Apashe\Black Mythology\01 - Black Gold.mp3
TF1:\Music\Apashe, Dabin, Kai Wachi\Black Mythology\02 - Forsaken.mp3
TF1:\Music\Mantis\Block Rocka\01 - Block Rocka.mp3
TF1:\Music\Kai Wachi\Echelon\01 - Echelon (Original Mix).mp3
TF1:\Music\Aero Chord\EDM.com Exclusive\01 - Bouzouki [EDM.com Excluisve].mp3
TF1:\Music\Aryay\EDM.com Free Downloads\01 - The Lawnmower by Aryay.mp3
If using the full path, with drive letter option, in .M3U playlist files then you can just tack on the #EXTM3U at the top of the file, and then the storage mount (in my case, it was TF1 since it was the first transflash slot being used and the device can determine which card slot to use when referencing the file. Just thought I'd pass this along for those that have devices with more than one storage location, and I thought I might start a thread on the X5 if there wasn't one already.
As an aside, I edited the files on my PC, but pretty much any text editor in Android or Windows should work with it, but you might have to check for / versus \ characters in the paths as it appears there were comments about changing these. Not 100% sure on that, but I've also seen alternate carriage returns used in Linux that get mutilated in Notepad and cause the file to be useless. I can't think of the specific character name right now, but in a *nix editor you'll see a square icon where you would have just had a normal carriage return. WordPad doesn't have this issue, so when I edit *nix files in Windows without access to something like Notepad++ I just use that.
HTH