You will have to excuse me but I don't quite get you ? Does aticonfig work with one card and catalyst says there's no drivers or it works with the one card one but doesn't ? I have come across the odd troubles down to a bug with acpi routing. You could try appending the boot line and adding
pci=noacpi
It's solved a load of weird troubles my end

That's odd: if I disable ACPI support in the BIOS I can't even boot, but you're saying to disable it at boot.