I would concur about the idea of playlists (or queue) with different sample rates of MQA.
my experience of the distortion has been when discovering new music via Tidal and flipping back and forth between different quality files.
Now most of the time I’m actually an album listener so with hindsight I am wondering if that is the main reason I’ve said I haven’t had issues when others have, so I started with 521 and never had a single issue, but was I only album listening? I can’t say categorically. I did use the same reference files as paulguk when I first got the amp, incl various FLAC files and MQA, and I also went as high as I could go with DSD too on a USB drive and from a UPnP server (Asset UPnP on a Windows 10 PC). I was switching back and forth between diff resolutions of Mozart violin conertos and I never heard any distortion then either,
When I switched to 705 briefly I was definitely in a new music discovery session flipping between things and it became very prevalent very quickly after the update so I went back to 521. Plus the 705 was somewhat “weedy” sounding
I’ve then really forgotten about the issue until 867 was seemingly forced upon me via chromecast and Google Home setup. now I don’t recall again having had mixed playlists and I think I’ve been album listening since, but 867 has again behaved for me with regard distortion. It does sound different to my ears compared with 521, but I struggle to described how. I hesitate to say it is better or worse though. My ears probably got used to 521.
On the “volume scaling” and max volume setting I see this issue definitely in the web client and not in the MusicLife amp control. It’s more pro in Ed of course the lower the max volume is set.
I’ve also noticed that MusicLife keeps messing with the DAC filters or maybe it is just displaying the wrong one….I set it to default apodizing on the amp and on occasion MusicLife will say different so I switch it back via MusicLife, I’m guessing that does have an impact (however subtle) on the sound qualities.
Cheers