I agree with Dragon. The set up you have seems overkill for MP3. Have you tried playback of Redbook CDs as AIFF?.
Server question, should I bother?
I generally listen to low rez downloads from Itunes or Emusic. I use a Macbook equipped with Pure Music, and an M2tech hiface Evo going to my DAC. I love the convenience of the Macbook and the Itunes interface. For this type of source material, would there be any real sonic advantage to switching over to a server and retiring the Macbook?