Add SLI mode in 2011-3 MB

[X-ray555]

Hello, friends! 

Tell me if i wrong, but as i understand, any x99 chipset supports SLI mode by hardware (there are few MB 2011-3 which support SLI mode, for example Asus Rampage V Extreme/U3.1, Asus Sabertooth X99, MSI X99A SLI KRAIT EDITION). But in this moment those MB are hard to get and they don't support some actual options like M.2 NVMe and etc.
The other way we have fresh chinees 2011-3 MB with M.2 NVMe and other modern options. Those of them which have more than one PCI-Ex16 slot support Crossfire mode, but don't support SLI mode (for example popular chinees brand HUANANZHI). 
Why is that? Can we fix this unfairness by BIOS mod?

Best regards, Denis.