if you don't have to store the music on the same machine you should look into a Windows Home Server running Squeezebox software and pickup a Touch or Transporter. The Transporter has a very good DAC section stock and there are many folks who have modded the Touch with good results.
Music Server/DAC in Same Box
Is there such a thing as a music server and a DAC in the same box? right now I have a mac mini Mach2music with Pure Music going into a Tranquility DAC but would be open to simplifying my system with a one box solution.