I found my Sony Walkman minidisc player in the shed and have dusted it off. It still appears to work, and the minidiscs are still in good order.
The problem is that minidiscs require a Sony application called Sonic Stage to transfer mp3's to the minidisc, and I wasn't sure I'd be able to find it.
Luckily there is an open source linux application called linux-minidisc available on github which is simple to compile and install and seems to work. So far I've only tested copying files off a minidisc. The files come off in *.oma format which VLC media player is able to read, they can also be converted to mp3 with ffmpeg.
I haven't had any luck transferring mp3s with linux-minidisc yet, it writes the mp3 but its not able to be played on my minidisc player.
You can get linux-minidisc from github using the following link:
It does require compiling if you aren't using debian/ubuntu, as there are no pre-compiled binaries for other linuxes. But the build instructions work well enough.
So linux-minidisc doesn't work for me, I've tried it on linux and also tried platinum-md which is another software project that is attempting to work with minidisc players. Sadly neither work for me, so I have reverted to using an old windows xp machine I have lying around and keeping it a long way away from the internet. I'll just copy things over via USB drive for the time being, which works well enough, but is just a little cumbersome.
The main issue appears to be my minidisc player, its a cheaper one that doesn't support the net-md way of copying data (I think)