Sorry to hear about the bad weather! It's pretty pleasant here in California right now, but almost 20 degrees (Fahrenheit) too hot on average. We'll probably start burning again, soon...
OK, so if the rack unit still keeps rebooting when the console isn't connected, it means that the problem is in the rack unit, so we'll focus on that for troubleshooting.
Since the behavior stays the same when using a different CF card, but changes when removing it, the problem likely isn't the OS installation on the CF card, but it's likely something inside the D8B rack unit.
If so, I'd first double-check all of the BIOS settings... could be as simple as that. If any of them changed from how you had set them, you'll want to put a new battery in there (how old is the current battery?)
If that doesn't help, I'd first try reseating all the cable connections for the Mud Duck system inside of the D8B rack.
And if that doesn't help... do you still happen to have your old spinning harddrive with the Mackie OS on it for troubleshooting purposes?
If so, I'd suggest to try disconnecting the Mud Duck system, and connecting your old spinning harddrive again, to see if it still reboots with that, or if it boots up successfully. That's to rule out the non-standard component (the Mud Duck system) as the culprit.
Since the reboot loop happens at a point where the Mackie OS started booting (e.g. after the "D8B 5.1 Realtime OS" logo is displayed) if I understand this right, I'd still think that it's most likely something related to the OS drive (or CF card/CF card system). That's why I'd check this first.
If you still have trouble after that, as a SEPARATE troubleshooting step (and only if what I'm saying above fails) I'd try booting with only one memory stick instead of 2 (...or if you use the old memory on the old board and you have 4 of these smaller memory sticks in the other memory banks, remove two at a time, and leave two in there... those need to be installed/removed in pairs). If it still keeps rebooting with that memory stick (or pair), try booting with only the other memory stick (or a different pair for the "small" memory on the old board).
Anyway, that's where I'd start.
Best of luck, and keep us posted