According to the 473 manual page 28, the AV OUT jacks output "analog video/audio signals selected as the input." (my emphasis) Unfortunately that suggests that indeed it will not output streamed music from those RCA jacks. This might be due to some copy protection scheme (although I can think of much better ways to make copies of your digital music).
Best thing to do is go to the Yamaha website and start downloading manuals. See if any of the higher/newer models will play digital sources over the analog outs. If not, you might need to upgrade to a model with preamp outputs if you stick with Yamaha. Also confirm that, if you get a model with preamp outs, that connecting them won't cancel your connected speakers.
I've noticed that some higher end Denons have dedicated RCA jacks on the back that say "Media Player Output." But I know nothing about Denons.