The best unmodded FW for music is most probably the Flyme 3.6.1A
Personally I’am using Flyme 4.0.5A with audio.primary.mx3.so lib (system/lib/hw) and soundfx from Flyme 3.6.1A. With this combo the audio output is powerful like never before, but the downsize is that with headphones plugged-in, the stock music player no longer can adjust the volume (either mute or full volume), but if you care for EQing and SQ, you are gonna be using poweramp anyway, which works perfectly. At the moment I’am listening to Bulletproof by Doctor P with my portable JVCs S500 at roughly 30% vol, cause at 50% it’s already above my comfortable listening levels. :)
I’am courious though what made the Meizu to lower the output in newer FWs? As far as I know they don’t have to comply with EU regulations. Or did they simply started using generic libs for compatibility reasons? Kinda lousy move I should say.