RAM Population with S2895 K8WE

Hello to all, I'm a newbie here!
I have a problem with my motherboard, I wonder if anyone can give me a help.

This is my system:
2 x Opteron 285
RAM Corsair ECC CM72SD1024RLP-3200
Windows XP 64x edition
BIOS v1.05

I tried to expand my RAM going from 4 to 6 modules of RAM (each module is 1GB).
Of course I populated slots like in manuals reference: starting from DIMMA1 and installing modules in symmetric way for each CPU.
By the way the BIOS keep reading only 4 GB instead of 6 GB.

Then I wonder if the motherboard can read also 6 modules or it only can read 2, 4 or 8 modules...

Can someone help me with this please? I wrote to technical support of Tyan but nobody seems to answer me

If someone has any idea about that, please post a solution!

Thank you very much for kind attention!