The Raspberry Pi seems like the best client, and you don't need an external DAC unless you're unhappy with the built in audio. One option is to use Moodeaudio on the Pi:
https://moodeaudio.org/.
An older PC, Core 2 or better, with the required disc space, Windows (preferably 7) & Foobar2000 as your "server". Foobar can be configured to stream to Moodeaudio (last post give the steps):
http://moodeaudio.org/forum/showthread.php?tid=88Both the Pi and PC support remote desktop so you can control all from pretty much any device. If you want the same music in multiple rooms play from Foobar on the PC, if you want separate music in any or all rooms play music from Moodeaudio. One option that seems to have been tested and works. Foobar plays pretty much any audio format and can convert on the fly to whatever the destination can play.