The eXtace audio visualizer (media-sound/extace) works perfectly fine on gentoo/sparc. Tested on a Ultra 30 with onboard audio using the kernel sparc audio drivers and esound with xmms as the audio source.. Please add "sparc" to the use flags for the ebuild. I am the maintainer of eXtace as well. (but I did not submit the ebuild)
Added. Thanks for the bug report.
Closing bug