All sources for this specific motherboard state that the ram limit is 8GB, however there was reports stating that the EVGA version of the nForce 790i ultra (reference board) was able to get 16GB of ram working.
So flashing the asus motherboard to the EVGA bios I was able to get 16GB of ram working on the asus striker II extreme. - so this confirms that this is not a hard ware limit and is in fact limited by the bios.
However due to the non-reference state of the asus board several issues occurred including no onboard audio, forcing me to run the GPU in PCIE 2.0 X16 slot 1 (which means covering a PICE 2.0 X1 slot used for sata port extension card) and most of the bios features being removed along with most sensors not reporting their readings such as heat and voltage etc.
With the above in mind I am almost positive that the asus bios can be edited to work with 16GB of ram - however I have no experience with bios editing (yet) I would presume it is a 'relatively' simple fix however I have no idea where to start, I am currently hard pressed for time and while searching for more specific terms of editing bios's for DRAM memory limit or similar I have not found anything - there are 101 tutorials around the internet for non-specific bios editing, so I can learn how to do some editing but hoping that someone may be able to point me in the area that would contain this information within the bios (a complete article on this area would be fantastic) - this way I could potentially compare the asus and evga bios to extrapolate the needed code/patch.
Further to this it would be extremely helpful if someone with experience could do this for me instead, however I fear the chances for this are slim as I really don't expect people to spend that much time on a problem that is fairly unique (thus the request for information first) but I could chuck a few £/$ (via paypal) for a successfully working bios edit.