I've just installed QuasarMX Beta on N9 PR1.1 and it works fine. Using Denon AH-C710 and the sound quality is very good. I am experiencing a few issues though. I hope we can talk about them in here.
All items are listed twice (after doing 'scan for music')
If the internet connection is set to "no background transfers" the player does not initiate a new WLAN connection but just infinitely waits doing nothing .e.g if I want to download an album cover or submit listened tracks to last.fm. If the internet connection is set to be persistent so the phone never disconnects from WLAN; stays always online, all works okay.
Downloaded album covers do not show instantly. The player has to be restarted (unless this is intentional, if so, won't be very useful).
Accepting album art from local files
Ability to change playlist order under the list view (the 3rd option)