Thanks for the review and the well researched information - interesting reading indeed.
I have both Plex and Subsonic as with a 1st generation Chromecast. I find Subsonic together with DSub on my phone/tablet to be a much better audio streaming solution than Plex. I've ordered a couple of Chromecast Audio's, hopefully with be with me soon and am looking forward to testing them streaming FLAC files from Subsonic.