I kind of railroaded myself into using calibre unfortunately.
I have a very specific filenaming scheme which I originally came up with back when I only used folders for organising my books in order to group together books that belong to a series but where the series is part of a larger universe.
Basically my folder structure is {World}/{Reading Order}; {Series} #{Series_Index} - {Title} - {Author}
On my kobo I have the autoshelf plugin installed which automatically parses this information when I add books and groups them together by world while filling out the series information.
In order to properly make use of this system I need to use Calibre custom columns and be able to export the books I want with this specific name format. I have yet to find a program other than calibre that would support this.
It would probably be smarter for me to reorganize my books at some point but I really like being able to basically drop a ton of books at once onto my reader using SFTP and as far as I can tell all common options rely on manually downloading the books, sending them directly to the reader or pulling them from their internal file storage in whatever form the application stores them...
I do like Audiobookshelf for the ability to add a book to multiple series, but the missing mass export functions stop me from switching
Two rack rails bolted together with a power strip and a tray holding my server mini PC. My router is bolted on as well to act as a switch for everything while also providing Wifi to my phone and laptop