For me, I run window server 2012 r2 in server core mode (and disable all unnecessary services). The reason I choose this OS since my player of choice, jplay, run its best at this os. I haven't try other os, but someone whom I know had tried other setup, including mac mini 2009 setup, and prefer this same setup as mine. I might try other os and system, if I had a spare time (which might be unlikely in the next few months). But I do welcome other input. I still would like to improve my setup if I had a chance.
So far, I'm quite happy with this setup. A few days back, I tried a fresh install of foobar portable 1.3.8 (and disable & delete all its unnecessary components & themes) and still found my preference lie on current setup. It offer the music flow analog and liquid alike, while maintain its black background, good imaging and great texture. Soundstage is the same.