Sound level variations Qobuz - up to about 15/20 dB, need to adjust preamp volume by track

Different labels have vastly different recording levels.  Reference Recordings uses lower levels to properly capture the very wide dynamic ranges of their classical music catalog.  Most popular music is crushed loud with no dynamic swings so it  screams at you.  When I hear that I instantly switch to a new record.  Playlists of different  selections are therefore very inconsistent volume wise.  If it's on the same record, which does happen, it's a mastering error.  Your better equipment now allows you to hear all that better than before.  You do need equipment with a remote control to adjust as required.

Folks have been requesting the volume leveling feature by Qobuz for sometime to no avail.  Tidal has it as well as Roon for me

It's frustrating.  I can't offer a solution but if you're interested, the origin seems to be from the Juke Box days.  Record companies discovered that "louder" tracks got attention and playback focus due to the "less loud" tracks seeming duller on the fixed volume playback of the boxes.  In this day and age I wish there was some kind of industry standard to keep things smooth.  Lots of engineers are still playing the "loudness game" when they mix 

If you've got a remote on your DAC, streamer or preamp surely it's not too difficult to adjust the volume as required.

Agree.  All media whether it be cd, records or streamers, volumes are different.  That's why we have remotes