Damn, this is completely legal in other countries, such as Denmark, you bought the media, you can enjoy it your way. RIP, backup or format shift as you see fit.

Have had this setup running for at least 5 years, works flawlessly, and running it in a docker container meant all I had to when moving to a new homeserver was copy the config file

How about you use eReolen which is the Danish library app available to all Danish citizens. It even incloudes audiobooks.