One thing I already have is plenty of 24bit DACS (usb and firewire) to use for the i/o into my system.
...
Like I said, I really don't care much for the iTunes software but I would rather stay in OSX if possible (but am willing to give Windows7 a chance if it behaves) so I might use a Mac Mini for the server duty, but I'm not locked into using
only Mac (but for professional use, it's Mac
only 
).
I just want a reliable and robust machine that will give me headache free operation and allow me to play music in the highest fidelity...
DACs are technically only 'o', and if you're planning to use USB or FireWire interfaces then you are building a jukebox, not a music server. Then, there's no networking involved, and you don't need any server software either.
The benefit of having a server, is that you can have a completely silent client doing the music playback. While my current computer is much better than the previous "hairdrier", it's not something I want in the room with me when I'm doing critical listening.
I was going to say that a PC is the easier way to go for finding the serving software. But if you're really wanting a jukebox type of configuration where the machine that holds the music also plays the music, then a Mac is perfectly suited. Doubly so, if it is a machine as quite as the Mini.
You just need an iTunes equivalent to pick your playlist, and away you go.
