I have bought a lot of music from https://www.hdtracks.com.
They offer high quality digital music in FLAC with high bit rates. More importantly, many of the recordings are remasters from originals which is the single most important factor.
To get the best playback you will need a digital interface from the PC to your amp (I use HDMI) and proper software. I use JRiver MC18 in "WASAPI Event Style" mode which completely bypasses the Windows mixer to deliver a clean digital stream to HMDI.
It all sounds pretty awesome with my Denon (pre-amp outs) to my ADA1000 and M80s.