One decision to make is whether you want the server that stores the music located in the listening room or elsewhere. There's a good argument for having the computer server located away from the music room but then you need to get the music from point A to B.
I'm fond of the now-discontinued Squeezebox appliances, but they are still available. They receive their data via wireless or ethernet, are easy to use, and work well with any SPDIF coax or optical DAC you could choose.
For a server, I have a small Vortexbox in the basement. It is low-power consumption and also headless, meaning it is easily controlled from any laptop or other remote computer in your house. I use a Kindle Fire to select and play music.