This small Dutch recording company
2L has compiled a set of classical tracks each available for downloading for free in several different formats, including Redbook (CD), up to 24bit/352.8kHz Hi-Res PCM, several MQA variants (including CD-quality PCM encoded with MQA) and several DSD variants up to DSD256:
HiRes Download - test bench
I have downloaded the files and now struggling to make my DietPi (Linux) Allo USBridge network streamer to pass through native MQA files and play them back on the attached Matrix X-Sabre Pro MQA. So far, no matter what I've tried nothing works. MQA files are in fact regular FLAC format files, so they would play as FLAC at 24bit/44.1kHz and the DAC would never attempt to MQA-decode them. Interestingly enough, DSD files when played back same way are properly recognized and played in native DSD mode by the DAC (they sound beautifully, by the way), so I am inclined to think this is a Linux issue. Linux developers does not seem to be interested in supporting MQA at all, so technical information is hard to find.