Well GsmArena says,'With pretty high
volume levels and nicely clean audio
output, the Galaxy 3 can easily replace your dedicated MP3 player'. So I don't think you really need to buy a dedicated PMP. Also the SQ of SoundMagic PL21 is just superb for the price but it may sound muddy out of the box. After 50hrs of usage the SQ will be crystal clear.
Samsung Galaxy 3 and Galaxy Apollo review: Galactic twins - GSMArena.com