Hello Adrian,
Yes, I tried booting into the older kernel from GRUB. In fact, attempting to load the latest kernel from the repositories causes the system to crash back to Open Firmware, as discussed previously.
However, you mentioned that all further discussion should be based on a known working image. Does the image I used fit this description?
I went ahead and tried this one: https://cdimage.debian.org/cdimage/ports/current/
-- Sincerely, Cedar Maxwell