You've just bought a BlueOS device, so why not use that? Roon (and arguably Plex) are marginally better in UI but ultimately sound quality at your ears is dependent on the room, the source and the DAC in that order, assuming the same power stage and speakers. Your speakers and power stage (and likely the DAC, though there aren't any published specs that I can find) are really good, but you'll still get an awful sound until you get a big rug down on the floor and acoustic treatment on the walls. Sorry if that sounds harsh but it pains me to see you spend £5k+ on hifi and not use it to its full advantage - otherwise simple low res streaming from spotify or google play will be perfectly sufficient!
Personally I'm happier supporting artists directly by spend £25 on new digital music each month and streaming it from a local source (or going to gigs!) but I can see the attraction of streaming :)