Even if there's not much of a chance for success, I'd still try to clone the OS onto one of the CF cards another time, in case something happened with the D8B, that shot the installation to hell during bootup, and killed it on both CF's when trying to boot from each one, without the Mud Duck system itself being defective.
Also, unless you already did so, I'd make sure to try it with the IDE ribbon cable you're using with your harddrive, and with a different power connector inside the D8B, if available. Just to make sure you check all the boxes/possibilities.
I never had a Mud Duck system, so I don't know what the options are (e.g. jumpers on there that may help to reset it... or just leaving it unplugged over night to let any "wrong charge" dissipate. This recently helped me with a Sonos ZP90, btw., where online forums said that the symptoms are certain death. It came right back to life, when leaving it unplugged for long enough).
If none of that works... I looked at the pictures for the Mud Duck system on Reverb, and the metal frame that goes in the place where the floppy was, has a StarTech.com sticker on it. I don't know if that's just for the metal frame or if it comes as an assembly with the CF controller board... but I'd look on the circuit board for something that looks like a model name, and search on StarTech.com if they still sell that...
I'm kind of curious now... my CF card is inside the D8B case. So, if StarTech still sells that thing and it's affordable, I might want to get one, too. Could you share a picture of the CF controller board here, that shows whatever writing is on it? Maybe I'll get one for myself (...or maybe I, or someone else would notice something that could be the cause of the issue).
Thanks in advance! Hopefully these CF controller boards are still available at a good price
