I will go with my converted library approach.
Or maybe wait if other forum members have some good ideas and suggestions?
A bit off-topic and on a strictly personal note:
Whenever I encounter any 24bit or dsd format files, I immediately convert them all to 16/44. (or 16/48)
I am personally convinced those formats bring no sound quality improvements whatsoever.
(and I have been accused of being an audiophile in the past, and I do own some 'seriously good' equipment)
And on my portable audio device I am perfectly content using mp3/320kbs or Opus at some lower bitrates.
I am guessing that same as you, the dac and the analogue components of the portable device, and the headphones (and/or lacklustre Bluetooth connection), and the listening circumstances will make it practically impossible to distinguish any relevant differences between e.g. even DSD256 and Opus > 256k.
Going from e.g. flac 24bit/192kHz to Opus 256kbps would result in roughly some 20x smaller file sizes.
So that's twenty
times more music on the same available storage space, without losing any noticeable sound quality!
That's not a difficult choice for me…