Many thanks, James. That is very helpful.
I'm confused about the purpose or benefit in setting up a scratch drive with the BR-20 (when the music library and artwork is on a NAS). Can you please help?
(The BR-20 doesn't seem to cache the resampled artwork files to the scratch drive as resampled jpg files are written to the NAS - 4,792 of them in my case - even when there is a scratch drive set up. Those files written to the NAS initially took me by surprise - though I can see the reasoning, especially if there isn't a scratch drive.)
Looking to the medium/long term, I would like to buy a spare Rasp Pi 4 board and just store it away somewhere as insurance in case of problems in the years ahead. Is the "Rasp Pi 4 B" board compatible with the BR-20? (I see that you have previously recommended 4GB memory.)
The BR-20 is very impressive indeed.
I'm slowly getting it set up in a way I prefer. Most of my music is classical and, very sadly, the "composer" tag isn't supported so I've had to copy all composer tags over to the album artist tags (mp3tag is a blessing) and then I had to rename all artwork to folder.jpg (where it wasn't that already) so that the BR-20 resampled jpg files don't totally confuse the other systems I use.