Hi Ifyrilei,
The short answer is this: Your motherboard BIOS is reporting to our software that it can support a total of 16Gb, but it is possible that it is reporting incorrectly. It is also possible that the documentation you have is out of date, or something changed with a more recent BIOS.
If you would like to upgrade your system with additional memory, I would recommend first checking with the manufacturer (downloading the updated documentation, or reading the BIOS change notes would be a good place to start) before trying to install more than the 8Gb of memory you know the system can handle.
I hope this helps, and sorry I can't just tell you which source is correct. Let me know if you have any other questions.
Thanks,
Kris