I used to have a Asus M2N SLI Deluxe motherboard.
That had a Am2 cpu socket. I know the board could support up 8Gb of DDR2 memory at 800Mhz
it had four DDR2 memory slots on the motherboard.
So if yours has four memory slots, and each can take DD2 memory it will most likely support 8Gb of total memory.
If the board only has two memory slots then the maximum amount of memory it will support and see is limited to 4gb total.
Trying to fit more than 4gb will result in the motherboard not posting, or will simply be ignored by the bios or still read as a 4gb total.
Edd.
Specs for your motherboard can be seen by clicking on the link bellow Edd.
https://www.asus.com/Motherboards/M2NXE/specifications/