Hi!

I own an Asus Pro WS X570-ACE, [link to ASUS Website Removed]

I bought it solely for Deep Learning setup (not mining, really, I do require a fair bit of PCIe bandwidth for computer vision tasks, but find PCIe 3.0x8 to be sufficient for RTX3090 and my training setup) since it is the only one I am aware of that supports x8/x8/x8 configuration (albeit in somewhat weird - for me non-understandable way - but in my case it works much butter than my ex MBO - MSI MEG X570 Unifiy (I have sold that one since x8/x8/x4 did not work as expected using my now-also-ex 3x1080Ti.

The board, using the same configuration, works flawlessly using 3x1080Ti and Phanteks 600mm PCIe risers [link to Caseking . DE removed], hitting every GPU with about 200 images per seconds for train, 600 images for testing (train is much harder since it requires gradient calculation...).

I have just bought 3xRTX3090 just to upgrade those elderly Pascals (or whatever those were) and BFLOAT16 + Tensor Cores is nowadays a must have for DL setup.

But you probably guessed it - my new shiny Asus board does not support changing PCIe gen changing, and it's stuck on PCIe Gen4. When I turn on the PC everything works just fine until I try to fire up nvidia-smi, then all hell breaks loose (errors start appearing in nvidia-smi). This is due to risers being incompatible with PCIe Gen4, and I simply cannot find 4.0 compatible ones of the required length (I am using Phanteks Enthoo Pro 2 with one GPU in main slot, two GPUs in "vertical slots" since it was the only case that supports it, not really intended for it but works just fine, since those 3090s are too big to fit one by another in slot directly). Every GPU in being first slot (without riser) works just fine, and ony other onlder GPU works on risers too (gen3, gen2 GPUS). The only BIOS option that the board offers is some kind of RAID configuration and is mentioning bifurification (disabled it, set it to x8 mode, but no genX setting support).

TLDR:
Could this BIOS be modded to support PCIe Gen3 setting? I tried multiple different BIOSes (including latest BETA one from ASUS - 3501)?
I am currently running on Ryzen 5900X with 4x32GB DDR4 3000 Corsair DIMMs, but planning on upgrading to 5950X some time this year. Power Supply - SuperFlower 2000W.

Let me know if you need any more info. I use this workstation with Linux/Ubuntu 16/18/20, but I see no problem using Windows to try modding this thing since I am a bit desperate - I need this setup to work.

Thanks so much in advance!