I installed rhythmbox-0.11.2-r1 on my ~x86 system. After the installation finished, I noticed that I was able to play songs, but I heard nothing. That was so, because gst-plugins-alsa wasn't installed (I'm using ALSA). After installing gst-plugins-meta and setting the alsa USE flag for this package, I was able to listen to music, because gst-plugins-meta pulled in gst-plugins-alsa. IMO, rhythmbox should depend on gst-plugins-alsa (or -oss), even if it is indirectly by depending on something like gst-plugins-meta.
rhythmbox-0.11.5 is now unmasked in ~arch and correctly deps on gst-plugins-meta. Closing fixed. Thanks