Ok, so clearly not an OS thing. You got it to work with a standard Android OS on a Samsung device. So my Sony Xperia shouldn't be an issue. Gonna check the formatting on the microSD card I use right now. Thank you!
UPDATE: Ok, so my card WAS formatted to exfat. Did you have any particular folder setup? I mean, was all your music in individual folders in the root? Or did you have it in "Music" or something?
UPDATE 2: To be safe, I copied out the music folders into the root directory. So ROOT -- ARTIST FOLDER, instead of ROOT -- MUSIC -- ARTIST FOLDER. It was formatted exfat, still didn't work. Now the manual does say it won't read FLAC but not all my files were FLAC so it should have read something. I will try with a USB stick, although having to convert a LOT of my music to mp3 will be a bigger nuisance than it's worth probably.