Pi DAC or Amp DAC??

[stree]

New to Pi and Pi for audio, but having a go... I have got a friend of mine intrigued and he is getting a B+ to set up a music player, to which end I sold him an amp I am not using......a Muse 7498, the one with USB and SD slot, WAV & FLAC player........He asked me something I was unsure how to answer, "The amp has a DAC in, why do I need another DAC on the Pi??"
Could anyone explain what the situation is here?