Thing is I've done all of that. It's a rather long process.Set your theme to one of the basic color themes or default/none, then try and load it up again.
First, I got an mp3 and ran it through Audacity to make it a wav file then when I imported it the counter on the import window showed 00:00:00 for start and 00:00:00 for the end so I went back and took the mp3 and ran it through formatfactory to make it a wav file then at the import window the song is ether shortened from it's original length like 2 minutes to 32 seconds or longer than the actual song causing the import window to crash.
Second, I thought that was okay if not what I preferred but it would at least play so I added it to my CN City theme and did default theme then went and loaded it up but it starts playing the bgm form a theme I didn't select from the Dragonball Super theme that's also on my SD card!