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Mkay. Not so good... Maybe if partitions are created not at the end of the disk it can screw the numbering scheme? But I don't know for sure. But that's not a big problem, you can fix this as I did that one time before.

Boot with your Linux Live DVD, open a terminal, go root with sudo su. Type blkid to check your partiton layout. Maybe your partition numbers are shifted now and you are seeing some /dev/sdaX with PARTLABEL="Extra" now. The important thing is to know which partition is your Debian root and which one is the yaboot partition.

I had a quick look on your yaboot.conf. Your root partition was the one with "UUID=926469b7-94af-4d34-8622-a13c249c59be". This should also be the case now. Now it's the time to edit your yaboot.conf on disk. Mount your root with mount /dev/sdaX /mnt/ where X has to be the correct partition number. Then edit your yaboot.conf with pluma /mnt/etc/yaboot.conf & or whatever the text editor is on your Linux Live DVD. I use Ubuntu MATE, so it's pluma.

Search for the root= line. In your case this is root="UUID=926469b7-94af-4d34-8622-a13c249c59be" which should still match the output from blkid. If not, change it accordingly to the correct UUID value of your root shown in blkid.
Next, check the partition= line above. The number must match the partition number of your root, e.g. if your root is /dev/sda8 then you should write partition=8 here.
Last thing left is to check the boot= line. This is not a Linux device path but an OpenFirmware device path. It's about the HFS-partition where Linux installed yaboot. On a system with only one harddisc only the partition number at the end matters, e.g. boot="blablabla-part3". The part number here must match the output of blkid too. If your HFS-yaboot partition is /dev/sda3 in Linux terms, then boot="blablabla-part3",

Ok, you are done editing yaboot.conf now. It's time to write the changes to disk with ybin -v -C /mnt/etc/yaboot.conf. Check the output of ybin if it wrote to the correct partitions and 'blessed' them. If everything was correct your Debian will boot again!

So, now you are an expert too. Here comes the easy part to add MorphOS as a 2nd boot option:
Edit your yaboot.conf again, adding macos=/dev/sdaX with X being the partition number of your HFS-MorphOS boot-partition. If you want to default to booting MorphOS add another line defaultos=macos. Write the changes to disk with ybin -v again (no need for the -C option here).

That's basically all the magic involved! For more detailed information you can type man yaboot.conf in your shell.