try reinstalling the drivers using driver cleaner 3 and make sure you leave all the settings to default, except the one setting that asks you if you want to use sli. Tell us how it goes.
man just add another gt to your system and you'll outperform a 7800 gtx 512. Then wait for the next generation super card to come out that can outperform your 2 gt's and buy one of them. But make sure it can beat them by a reasonable margin or there is no point in wasting your money. Since...
I'm not sure if you'll have to change any settings in the bios, cause I didn't. But you have a different motherboard. It looks like you've covered pretty much everything. You obviously also know to put the sli bridge in there as well. Yea other than that you'll just have to check a little box in...