Easy Windows App for Flac & AIFF for Novice

Boy you don't want much do you. Best is subjective. Windows has built in. VLC, Foobar, many more. What's UX. If sound quality matters then don't use BT, it's the great equalizer that will degrade most music regardless of the player.

Foobar with Fidelizier  is hard to beat  for sound quality if you want to run it as a dedicated music server .  The UI is a little clunky but there is lots of support on the interweb.  Fidelizer depending on the settings makes sound top priority at the expense of other applications but it can be set to not start automatically on boot.

Suggest you may want to  check out JRiver Media Center as well.

Logitech Media Server works well I'm not sure how it compares to JRiver or Foobar I went from it right to the Auralic app.

@jaybe VLC is a great idea. I have used it for video but never thought of it for audio playback. 
FYI, UX is user experience. 
I totally agree with you about the weakness of bluetooth, but this isn't for me, it's for a friend who will only play via a bluetooth speaker, not a hifi system. Thank you. 

Thanks guys for the other suggestions, but "clunky" is the opposite of what I'm looking for here. Jriver is too costly, I saw there's a newer free "Jukebox" version...it has no images which seems basic and expected these days in any music app. 
LMS via Squeezebox was my go-to around 1995. From mentions here, I get the impression that it hasn't changed much this century, lol. Maybe that's plan B if VLC doesn't work out. Cheers,
Spencer 

Great UX experience and while not a Windows solution works really well controlled from a PC  Volumio and a Raspberry PI.

For under $50 with the power supply and the free version of Volumio It's an outstanding music server and an inexpensive way to share USB hard drives across a network.

Setup is pretty strait forward.  I'd still be using it if Amazon Music would have released the API