The brilliant software team who brought us Sooloos was spun out of Meridian a few months ago to form Roon Labs (https://roonlabs.com/). If you haven’t yet tried Roon you really should. I’ve used a bunch of different media servers and control points over the years and believe these guys are really going to shake everything up.
Today, you can play music to Volumio using Roon and AirPlay, but this is of course limited to 44/16. The team seems very interested in using Raspberry Pi as a renderer (see https://community.roonlabs.com/t/raspberry-pi-support/1129/18) and is working on a “Roon Speakers” network protocol for streaming over LAN (see https://community.roonlabs.com/t/roon-speakers-what-when-how-and-for-whom/290). They plan for this to fix all the ugliness of UPnP, AirPlay, etc. and ultimately become the gold standard.
Anyway… I just wanted to put this on people’s radar and see if anyone was interested in or already working on writing a upmpd-like daemon for RoonSpeakers that bridged it to MPD?