Look at those baby radiators! Very cute!
Coincidentally, earlier this year I built my own custom loop machine using an ASUS W890 SAGE SE motherboard, Intel 658x CPU, and a SilverStone ALTA case (I used a D1 rather than the T1 - as I already had it available).
Mostly out of necessity, I went with a Watercool MO-RA IV 600 external radiator with 9x Noctua 200mm fans. I was pretty sure the ALTA D1 did not have the room to fit dual PSUs, the necessary radiators, and all the hoses to plumb everything together.
It was honestly a pretty painful experience to get up and running - for a variety of mostly self-inflicted reasons, but it works great now. I highly recommend the MO-RA, it is a fantastic product and works exceptionally well. Having your radiator, pumps, and reservoir all be external greatly reduces the stress and headaches of building a complicated rig and trying to fit everything neatly inside the chassis.
I would highlight one issue I ran into, that may be applicable to your build:
My build has two H200 water blocks and the one CPU water block. (All the water blocks are from AlphaCool)
I originally was using a EKWB 2CPU 4GPU manifold, configured to be fully parallel (so out to the 2 GPUs and the CPU in parallel, back in from the 2 GPUs and the CPU in parallel). This worked great for about a week, but after things settled my GPUs started running hot due to not receiving sufficient water flow.
In my case, the GPU water blocks are, by design, far more restrictive than the CPU water block, so in a parallel configuration the coolant was taking the easiest path through the CPU block and was starving the GPUs. Initially it seemed OK, but after a bit of time I had some debris or build-up accumulate in the GPU water blocks and this parallel config amplified the problem by sending even less coolant flow over the GPUs.
My manifold does allow for putting the CPU and GPU sections in a serial config, while maintaining parallel amongst the GPUs. However, after debugging this problem I just went to a fully serial configuration (partly for simplicity, partly because this ALTA D1 case doesn’t leave much room for the manifold). I use quick-disconnect fittings between each device, so that allows me to easily repatch things into whatever layout is needed.
With my serial config I see around 186L/h flow rate. It is hard for me to list the cooling performance as I don’t track ambient temperatures effectively in my room - but highest GPU temp I see (with both running at 600W for >1 hour) is ~30C over ambient (so typically around 52C on last GPU in the series) and CPU is similar under load.
I am hoping to add 2 more GPUs next month (assuming I can still source them) - so fingers crossed this setup will handle an additional 1200W of heat generation. If you were able to run those 4x RTX PRO 6000s with your radiator and pump config - I am guessing the MO-RA IV 600 should handle it as well.
As you can see from the pictures, the ALTA D1 is a tall case (which is very nice!) but also a pretty narrow one (which is not so nice with a big SSI-EEB motherboard). Insides are not so pretty, but it is functional.
I am considering switching to a single 3000W PSU (I have my eyes on the ASUS WS3000 you used in the video) and putting it in my Define 7 XL case. This would give me a little bit more room to reduce clutter. But, I will need to redo all of the hoses and fittings to make that move - so it is not high on my TODO list.