Sound cannot be mixed in f9

[lmaxmax]

My sound card is detected as MCP51 High Definition Audio.

**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 0: CONEXANT Analog [CONEXANT Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 1: Conexant Digital [Conexant Digital]
Subdevices: 1/1
Subdevice #0: subdevice #0
(The device 1 never works)

And when I play the music with one player, it works fine. BUT if I open another player to play music simultaneously, the second player has no sound or just crashed(such as realplayer11). The realplayer crashes report which may be useful is attached.

Any ideas??

Thanks