Does a proper dual SP3 workstation motherboard exist?

You can use Rufus or have a previous installed windows to by pass the check

When I briefly considered a custom loop, I considered having a custom block milled for VRMs. You may be able to find a VRM block for your board, though. Otherwise, most (all?) dual SP3 boards are really designed for front-to-back airflow. You can achieve this by putting your radiator at the front of your case, and drawing in air through the radiator.

Yeah, it’s stuff like this that took me away from water cooling relatively quickly.

If you plan on doing a serial flow from one chip to the next, you could use the second chip’s header to control the radiator fans, as the second chip will always be a bit warmer. Otherwise if there aren’t any parts out there that do this already, it’d be pretty trivially easy to write a bit of firmware for an arduino device to allow it to take two PWM signals as inputs and output a PWM signal that matches the input with the higher duty cycle.

If you have an oscilloscope, you can also check the alignment of the PWM pulses on the two fan headers. If you get lucky and they make use of a synchronized clock, you can use a simple OR gate instead of an arduino.

You could definitely use dual AIOs, but that would be $$, and you’ll need room in your case for two relatively large radiators.

I think honestly even if you get it rigged up with very quiet cooling, you’re likely still not going to want to be in the room with this thing while it’s cranking. Just the chips alone are configurable to up to a 280W TDP. So that’s 560W of power that will be dissipating into your room just from the chips alone. You’ll also have your GPU, memory, PSU, and various other components adding lots more heat dissipation on top of that.

To get a feel for what this is like, grab one of those smaller travel hair dryers, turn it on in the room, wait a good 30-60 mins (or however long it takes for the room temp to stabilize), and see how you feel with the temperature in the room.

You might be thinking “nah, it won’t be that bad because it’ll sit idle most of the time,” in which case, I’d maybe wonder whether it’s worth the expense vs something like a 7950X build. Most of these problems that you’re running into don’t have well-tread solutions because most people house these in racks in air conditioned server rooms, and they generally attempt to keep them as uniformly loaded as possible.

If you’re hell-bent on using this as a workstation, maybe consider going the Linus Sebastian route and house it in some other room, but run a fibre optic thunderbolt cable (and maybe also an active fibre optic displayport cable, depending on your display needs) into your office so that you can be “sitting at” the workstation but not have to deal with the noise and heat.

I was indeed thinking about optical display / KVM, but about a different type of device and then more about piping powerful compute to our family room for gaming won’t happen soonish I think.
I have a lot of other projects to take care of first. It may be that the computer eventually gets relegated somewhere else.

FWIW the Asrock Rack board is available right now.