I finally managed to get the Gigabyte M57SLI-S4 to boot LinuxBIOS today. Turns out that some kernel boot parameters were required to make it do the right thing with the IRQs.
It’s not perfect yet: the network interface doesn’t work, there’s no ACPI support, the USB debug device support needs to be disabled (probing for the device adds a lot of time to the boot), and I’m still working off Yinghai’s fork of the code, because it has not been merged into the V2 tree completely.
But we’re making progress