Okay - this is getting too complicated and I went through something similar to what you are trying to figure out. In my old system, I had my computer feeding my integrated amp (with a DAC) directly via USB cable. In my new system, the computer is across the room and much too far for a cable (and how to route it). I looked at various solutions (including a Raspberry Pi) and finally settled on the Bluesound because it does everything you are describing. Please note that the Node 2i is not dependent on Airplay (that is just a convenience factor or if one wants to play through the phone/tablet only). One can use the computer to play through the Bluesound (at full resolution) or through the Bluesound app (again at full resolution, as long as it is on your computer - files or, say Tidal/Quboz desktop app) all over wifi.
BTW, this is a killer deal: the Vault 2 (which is a Node 2i plus CD ripper/storage) for $600
Rip, store and stream your entire digital music collection in lossless formats without ever turning on a computer! The VAULT 2 is the heart of a modern digital music ecosystem. And with Gigabit Ethernet connectivity, you can put the player anywhere in or out of sight, and stream your music to...
www.bluesound.com