You are first with ASUS Dominus Extreme motherboard I heard.
I'm jealous on you definitely. But let's say like this... in my part of the world building my computer need same effort as building Dominus Extreme and Intel Xeon Platinum in United States. There I would have 6x 16GB DDR4 and Domunus Extreme 100%.
Where you live? If you live in Europe you can buy EVGA 2000W PSU.
If believe EVGA 1600 T2 will be enough for single GPU, motherboard and processor.
I think ASUS Support here should be better, this forum is in clinic death.
They should say what they thought during build about Power Supplies and Dominus Extreme, dual motherboard, single 1600W, or ...?
Lian Li PC-V3000 could be modified probably easy for dual PSU.
And it's nicest Full Tower case on market.
Lian Li PE-01B - Power Supply Mounting Bracket
Or you could only cut other side.
But that's Rolls Royce among PC Cases, full aluminium and build quality and precision of work and finish is unmatched with any PC case at the moment.