Memory comparability issue with gigabyte EP45T-UD3LR motherboard

I purchased 2x viper 2x4GB KIT DDR3 UDIMM PC3-12800 1600Mhz ram to upgrade an old computer to maximum supported dual channel ram (16GB) from dual 4GB Corsair kit. When I install the ram either single stick or dual mode the bio is not recognising the ram. Can get to windows with both Corsair and patriot ram installed but system reserved ram is 7.5g (unusable). It is also not showing as dual in cpu-z. I have tried adjusting fsb from 1060 to 1600 (stock is 1333 for this CPU) and adjusting ram voltage (up to 1.58v) but still can't get the bios to utilise the ram. I tried enabling xmp in the bios. It seems to be recognising the timing so have not messed with that. Is there anyway to get this ram to work with this motherboard? I have read online that the Intel P45 chipset can only use low density ram made of 256MB ram chips but seems to be some debate. Is there 4gb pair ram that can be used in this mb? Support ram list is very outdated on the gigabyte website. Bios versions: F12e Cpu:Intel Core 2 Quad Q8400 Code Name: Yorkfield. Max TDP 95.0 W Current ram: 2xCM3X2048-1333C9DHX XMS3-1333 2048MB 1333MHz 9-9-9-24 1.50V ver9.1 Regards, Evan