There are several setups that feature high end server/DAC systems that you could not demo anywhere else.
if cost is a concern, you could put together a music server system yourself for a lot less than what a prefab box would cost you.
if/when i get around to building myself a home entertainment server, i'll build myself a middle-of-the-road box with a quad core, a couple of high-end large capacity hard drives, a top-flight video card - and an external soundcard, like the Presonus Firebox (firewire, out of production but i already have one) or the Audiobox USB (
link). studio-quality external soundcards such as these will have high-quality DAC converters. Focusrite and Apogee are two other brands to look out for. these external boxes may be overkill since they allow both playback and recording, but i'm not aware of any studio-quality boxes that do playback only. having the soundcard outside the computer maximizes your bang for the buck: the inside of a computer is a very noisy place, electronically speaking, and you need to put a lot of design into achieving high-end audio inside the case. external boxes don't have to worry about that, they have their own shielding/isolation... plus they can be physically placed far away from the spinning hard drives, noisy busses, etc.