Adding Mplayer is easy. Once it’s installed you can use the AlienBBC plugin or play wma files from Windows Media Player. You can play wma lossless files and also aac files from iTunes.
Go to the VortexBox command line by attaching a keyboard and monitor to your VortexBox or use SSH. From command line type
setup-mplayer
Wait for the process to complete. You will need to restart SqueezeCenter by rebooting your Vortexbox or typing this from command line.
service squeezecenter reload
Note: The way your router is configured can stop Real Audio from working.
Go into your routers settings page and select Advanced -> Firewall -> Application Level Gateway (ALG) Configuration and disable RTSP.