Mostly classical but many free high quality music in different high res formats:
dxd, stereo flac in multiple sample rates, 5.1 flac in multiple sample rates, and multiple dsd formats.
Nices test bench
Open web-site and enter top-right side of screen: 2L Brand Store / Test Bench HD audio files.
Note that you have to login with a default user as specified at top of this page.