I currently have 2 8TB drives and they are about half full, I've bought 3 more 8TB.
I do have a desktop(Win10), but when I said I had no option it's because I don't nearly have the space on it to do the transfer.
But I was thinking the following may work, that I haven't thought about before;
1. Setup 2 new drives on the desktop, doesn't need to be in raid, I can split the data if needed
2. Transfer the data from the the old Stripe on the server
3. Undo the BIOS raid on the server
4. Setup UnRaid like I planned before with 3 drives, 1 will be the safety drive
5. Transfer the data from the desktop to the new and fresh server
6. Move the 2 drives from the desktop to the server and add them to the UnRaid pool
Could this work? This will mean that only 1 of the operating systems on the server will need access to the controller, and neither UnRaid nor a Windows VM would need to read the Stripe somehow.