Serious question- what benefit do you get out of this? I had an SLI setup with Linux for awhile as well, before realizing that the second GPU was never being tapped into at all. It's recognized, and is getting power, but it's wholly under-utilized (if at all).
From everything I've found, Linux doesn't benefit from SLI nearly as much Windows can.
I've used several multi-GPU (up to 8x K40) Linux machines, and if your application can provide enough GPU work (say ML/AI, or physics simulations, etc.) they scale perfectly. For gaming, I don't know, but could be GP is doing non-gaming stuff.
What do you play on it?
Probably freeciv or openTTD, but on medium settings.