I have been playing about myself on my Curve9300, Using OS6.0 and Windows Media Player 11(Vista). I have made some progress by setting up Music WiFi Sync as normal to the point where you have the 10,000 songs on your berry. Once done close the BB Device Manager.
The music library file stored on my computer at:
%appdata%\Research In Motion\BlackBerry Media Sync\MediaSyncLibraryWMP.tle
I have copied this file and renamed and replaced the file on my Berry with it: Drive:\BlackBerry\system\PIN00000002.tle
ReBooted the phone and done.
This has given me access to all the files in my windows media. The only downside I have found so far is I have lost the album art. Is there any known way to solve this?