At home, I primarily use Plexamp running on the PC, with access to all my offline media stored in a Plex library (mostly FLACs). It can be controlled directly on the PC, or remotely via the Plexamp app on a phone/tablet.

I also have my docked Empeg Mk2a feeding audio into, and then back out of, the PC.

The PC audio is output via a digital optical link to a mini-system on my desk with decent speakers, and also via digital coaxial into a nearby in-wall CATV outlet.

I then have a splitter at the house's CATV distribution board to feed that signal back to a couple of other outlets, which then connect to the home theatre amp in the living room, and another amp in the bedroom, both with digital coax inputs. This means I can listen to the digital output from the PC in either of those locations using the existing in-wall wiring, just by switching to the correct input.

I think in theory the impedance(?) of the in-wall CATV coax isn't quite right for digital audio, but in practice it works perfectly. (The CATV cabling isn't used for any other purpose).

For anything I don't have available locally, I also have Spotify on the PC which again can be controlled via any phone/tablet, and also all three hifi/amp systems support Spotify Connect if I want to 'cast' directly to them if the PC is offline.

In the car I use my phone via Bluetooth, which is 'good enough' quality. Music sources are again either Plexamp, which can stream any content from my home library over the cell network, optionally transcoding the FLACs to lossy formats if I want to save some cell data (and there's probably not much benefit in lossless played over Bluetooth), or Spotify.