LMS is Logitech Media Server, think of it as a replacement for moode, although it's open source and is packaged by different distributors, piCorePlayer, MaX2play etc
I run LMS (piCorePlayer 3.20) centrally on an Rpi3 running only LMS , this references my NAS library, and also Spotify account (via another open source API called spotty). You can make this a stand alone player or, as I do, have it feeding multiple players/streamers, in my case a mixture of SBTouches, and RPis, amongst which is pi2 with an IQaudio HAT.
Integrating your FLAC collection and streaming services at the music server/LMS means that all sources are available via the same playlist on the same streamer...or any of the 4.
P.S. there's a new plugin for lossless radio paradise available for LMS too
All controllable from a smartphone/tablet app, browser, IR SB remote, or finally SBtouch screen...spotify just appears as another catalogue, you don't have to switch to a spotify interface...