Ya está!! Al fnal e probado con otro reproductor :D
Código:
<object type='application/x-shockwave-flash' data='player_mp3_multi.swf' width='200' height='100'>
<param name='movie' value='player_mp3_multi.swf' />
<param name='FlashVars' value='mp3=mp3/".$row['mp31']." | mp3/".$row['mp32']."' | mp3/".$row['mp33']."' | mp3/".$row['mp34']."' | mp3/".$row['mp35']."' | mp3/".$row['mp36']."' />
</object>