after so many failed attempts using downloaded drivers and changes with xorg.conf (TwinView option), and with no luck with "xrandr", I decided to try and give the nv driver a second chance. With a little bit more research, I found out that with nv open source driver, you use an option called "dualhead" and not "twinview". Gave it a shot and boy oh boy oh boy. IT WORKED!
The settings that did it for me for those who want to know:
Section "Device"
Option "DualHead" "True"
EndSection
Section "Screen"
SubSection "Display"
Virtual 1280 1024
EndSubSection
EndSection
There are more entries on these section of course but these are the ones that made it work.
By the way, the main reason why I wanted xrandr to work is for me to have a ONE BIG SCREEN. Two 2560x1024 (Two 1280x1024)