In case you are interested in other options which involve your Pi and some free time:

If your amp has HDMI input, you can connect the Pi and that is it. Else there is some neat hardware out there from places such as HiFiBerry and IQaudiO and others which can give you a high quality DAC to connect your amp, with an optional little Class-D amplifier to drive speakers directly (for other projects).

Once you have that connected there are lots of software options such as PiCorePlayer and Squeezeplug (Squeezebox Server) or Volumio and Runeaudio (New Projects). All of these allow you to control your music with an app or through a web browser.