Just to give feedback on this subjet, i am using now SongPlayer and indeed the sound output from mp3 is much better than with AmigaAmp and AHI, using 44 KHz and stereo from 196Mb/s encoded mp3.
However, there is still a minor problem: for exemple, Madonna seems to sing as if she has hair on her tongue (it means in french "avoir un cheveu sur la langue", not sure of the english for this expression), so that any "s" becomes "sssssss".
Maybe Paula is not able to make better, but it is still not perfect output.
PS: i am still using my Apollo 1260, now at 66Mhz.