After a good fight I finally won. The Uefi of the server is configured in HBA, PCIe pass-trough is available, boot drive is ZFS mirrored and next step is enabling ProxMox passtrough support.
Re-uploaded all the iso files for the VM's setup and everything goes smoothly, upgraded The Uefi / Perc / Idrac / Lifecycle / Nics / SSD's cmos.
I completely canibalized the second machine and upgraded the ram to 512 Gig moved the trongest processors, took the 2 SSDs and configured them on the back plane. Drives must be "industrially" dod wiped off before any use with these controllers, and it takes a looooong time. So I have a spare motherboard, one back plane, 2 server network adapters, 1 front panel board, 1 card reader, a vdisk controller and 2x750W power supply in reserve.
Not bad at all for a mere 1400$, considering the value of the parity ram and SSD's alone 4x1TB sandisk X400 + 16x32 gig error corection ram, that alone relaims a large part of the total price.
I also reconfigured and put on line the whole idrac and lifecycle infrastructure.
The setup is going to be awesome. It's going to be a Network file sharing with TrueNas, media server with Emby on linux, and my Personnal HAL 9000. All running on their own platform in the same server. A lot of fun for an old IT guy at home.
Finally I think the exciting part is close ahead. Never be too confident. They are sneaky machines.
But the light is visible... Going to start to get into the interesting part soon.