I do not have a N9 but a N900 and it made me discovering Rockbox. As a walkman-man generation I can say that Rockbox is the most evolutive player I ever seen so far. If I could have it on my own pc, I'll do (the last version of gmusicbrowser sattisfied me at least).

Try Rockbox and any other player will seem a toy.

Not only a good renderer, not only gapless, but playlist management in real time is a must (eg you can delet or move the next song on the current playlist, or add a song permanently or just the time it plays) Realy if someone can port it, it's THE BEST player for music lover.