Salvatore: thank you for the photo but I don't want to use an adapter, it just adds clutter and besides my computer already supports SD cards (or at least it should).
Anyway… So I put the files on a USB drive, copied them to to the appropriate folder, and …
Restart 1: …restarted the computer. The only difference I noticed is a blank icon on my workbench named SD0: that looked like a solid color grey rectangle. After that, I inserted my SD card but nothing happened. Clicking on the SD0: icon opened an empty window. I tried to access the SD0: through DOpus too but same thing.
Restart 2: So another restart, this time with the card in the slot from the beginning. I tried to format the grey icon using the AROS/AspireOS Format Disk tool, but it just threw a "Operation not implemented" or some such message. The Format Disk tool claimed the capacity of the SD0: is 0 kb or something weird. I tried taking the SD card in/out to see whether it'll trigger any prompts but no.
Restart 2: Then I restarted again. Same results (can't open, can't format). In the CLI I tried to "mount sd0:" but got the message the device already exists. then I typed "sd0:" but got the message the device is not mounted. Makes no sense to me… I unplugged the USB drive just to see whether that'll have any effect but no (except the standard Poseidon window popping up). Unplugging the USB drive made the SD0: icon disappear too!
Alright, I decided to delete those two files to get rid of the grey icon and retry this whole thing from the beginning when I have more free time. I'm sure the cards are Fat32 but will confirm that too before attempting this again.
So that's where I am right now, I'll try to poke it a bit more during the weekend and report back.
Thanks for the help guys!