As you said, there were no tips in that FAQ to do with the media tag...
I tried (without the spaces)
[ media ] link to an mp3 [ /media ]
and
[ media = link to mp3 ] text [ /media ]
Oddly enough when you just put the MEDIA tag round an mp3 and submit the post, it adds in an equals for no apparent reason.
It certainly does not recognise the media tag because it doesn't realise the /media one is the closing pair.