I did s'more experimenting and it turns out that Decibel's support for CD audio playback works just like Rhythmbox -- you can use either the libcdio or cdparanoia gstreamer plugins. Here's the updated info for the RDEP: cdaudio? ( dev-python/cddb-py || ( media-plugins/gst-plugins-cdio media-plugins/gst-plugins-cdparanoia ) ) cddb-py is still required, but either of the gstreamer plugins will work to get working CD audio playback. I personally recommend libcdio, as cdparanoia has been mostly broken recently; it often won't correctly access drives (even those via AHCI and libata, see bug 221145).
applied, thanks :)