I am testing out Xfce on Solaris in a SunRay environment (thin client). The problem with xfce4-mixer is that it seems to have /dev/audioctl hard coded. The correct way to get the audio device on Solaris (especially in a Sun Ray environment) is to use the $AUDIODEV environment variable. If this can be incorporated into xfce4-mixer, that'll be great.
it does that. See line 214. Please reopen if it's buggy (I don't have a solaris installation, can't test).