chamaeleon

I don’t use Calibre for this (but I do for epub and pdf ebooks). I use Plex and use Plexamp for my music collection. For audio books I used to have Chronicle Audiobook Player installed (which is open source, but not actively maintained) but am now trying out Listen Audiobook Player (which is not open source as a heads up). Both of those allow me to download books wherever I am.

If you have no interest in running a Plex server neither of them are suitable for you, but I just wanted to mention this solution in case you’re not dead set on using Calibre. Plex has a cost factor which may come into play (an obvious non starter for some). I have had Plex Pass for a long time so it was natural for me to use it, but might not be for you.

Plexamp is my primary music playback in the car commute if I’m not listening to an audio book. Love it.

Proxmox with a bunch of small dedicated lxc containers (running small Ubuntu lxcs mostly). It works for me anyway, though I don’t use any of the rr programs. My Plex lxc gets its Media files from an openmediavault NFS mount (Running in a VM instead of lxc), and I use smb file sharing for my windows desktop to access the same files. Your mileage may vary, what works for me night not be for someone else.