Could the NAS input/recommendation from Taiko be part of why they suggested it? Using a NAS eliminates what you have explained/shared...I could setup a Ubuntu machine and do the conversion there, with a version that recognises both the formatted disks but, it’s another conversion, where we always loose something. Silly me, it’s an obsession.
I have in the Taiko Router network, a windows home server, assembled in a Pink Faun ancient streamer, great PSU BTW, not exactly a NAS, but that would be the longest path. From the Router it will be the shortest path. Just a little bit OCD…, but I’m getting better.