Hi,
I am using openSUSE 11.0, gnome. Mplayer has decent sound, but smplayer has much lower output. Vlc (version 0.9.8a) has no audio. Even banshee (version 1.4) and amarok (version 1.4.10) have low audio compared to windows players. I have packman, oss, non-oss and updates as repos.
Also, note everytime you start a multimedia app, there is a chance your PCM volume may have been reset to a low volume level, and it may be necessary to adjust it.