Wouldn't it be a better idea to use a minidisc player with a digital out (like my old Sony MDS-JB940) and feed that output into an interface with digital input or into a recorder with digital input?
I think keeping it digital is a great idea.
That said, all the analog transfer methods with this modern gear will surely work fine, and likely exceed the quality of the original MD media.
If you do an analog transfer, save the originals, so you can do a digital transfer later, once you realize how much better it might be!?!?
but yeah, don't let perfect be the enemy of finished!
If it's just one or two discs, not really worth sourcing a digital machine... Hundreds? Perhaps.
One potential advantage or recording to the SD card is that you won't have any interference which might be caused by having a computer plugged in. Suggest running off USB power pack to avoid this, but they might have little computers in them which make noise too!? Wall wart? Also a switching power supply...
Another advantage of using the SD card is you can use the Wingman app to connect to the MixPre and set the file name each time you change discs. It only takes short names though.