The Raspberry Pi isn't known for its audio quality, but that doesn't mean you can't get a little more bang for your buck from it. RaspyFi is a custom Raspberry Pi image meant to make your audio sound better.
RaspyFi uses a custom disk image and a USB DAC (one of these is probably a good place to start). From there, you can configure your audio output quality and mixers, amongst other features.
You can then point RaspyFi to a USB drive or a NAS to send that music to your devices. We haven't had a chance to dig into the distro too much, but as a proof of concept alone it's worth checking out if you're interested. You'll find all the instructions you need over on the RaspyFi site.