Два монитора

Как точно -- врать не буду, не знаю. 
Могу привести свой конфиг техз времен, когда на Matrox G450 использовал 2 монитора на одной карте. В этом конфиге есть интересная деталька -- 
каждому экрану сопоставлен PCI ID карты (узнавать из lspci). У меня обоим экранам один ID, но ты можешь попробовать разные...

Итак, конфиг:

Section "ServerLayout"
        Identifier     "Matrox PowerDesk configured."
        Screen         "Display 1" RightOf "Display 2"
        Screen         "Display 2" 0 0
        InputDevice    "Generic Keyboard"
        InputDevice    "Configured Mouse"
EndSection

Section "Files"
        FontPath     "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
        FontPath     "/usr/lib/X11/fonts/misc/:unscaled"
EndSection

Section "Module"
        Load  "GLcore"
        Load  "bitmap"
        Load  "dbe"
        Load  "ddc"
        Load  "extmod"
        Load  "freetype"
        Load  "glx"
        Load  "int10"
        Load  "record"
        Load  "vbe"
EndSection

Section "ServerFlags"
        Option "Xinerama"
EndSection

Section "InputDevice"
        Identifier  "Generic Keyboard"
        Driver      "keyboard"
        Option      "CoreKeyboard"
        Option      "XkbRules" "xfree86"
        Option      "XkbModel" "pc105"
        Option      "XkbLayout" "ru"
        Option      "XkbVariant" "winkeys"
        Option      "XkbOptions" "grp:ctrl_shift_toggle,grp_led:scroll"
EndSection

Section "InputDevice"
        Identifier  "Configured Mouse"
        Driver      "mouse"
        Option      "CorePointer"
        Option      "Device" "/dev/input/mice"
        Option      "Protocol" "ImPS/2"
        Option      "Emulate3Buttons" "true"
        Option      "ZAxisMapping" "4 5"
EndSection
Section "Monitor"
        Identifier   "Display 1"
        HorizSync    30,0 - 70,0
        VertRefresh  50,0 - 160,0
        Option       "DPMS"
EndSection

Section "Monitor"
        Identifier   "Display 2"
        HorizSync    30,0 - 70,0
        VertRefresh  50,0 - 160,0
EndSection

Section "Device"
        Identifier  "MATROX CARD 1"
        Driver      "mga"
        BusID       "PCI:2:0:0"
EndSection
Section "Device"
        Identifier  "MATROX CARD 2"
        Driver      "mga"
        BusID       "PCI:2:0:0"
        Screen      1
EndSection

Section "Screen"
        Identifier "Display 1"
        Device     "MATROX CARD 1"
        Monitor    "Display 1"
        DefaultDepth     24
        SubSection "Display"
                Depth     8
                Modes    "1024x768"
        EndSubSection
        SubSection "Display"
                Depth     16
                Modes    "1024x768"
        EndSubSection
        SubSection "Display"
                Depth     24
                Modes    "1024x768"
        EndSubSection
EndSection

Section "Screen"
        Identifier "Display 2"
        Device     "MATROX CARD 2"
        Monitor    "Display 2"
        DefaultDepth     24
        SubSection "Display"
                Depth     24
                Modes    "1024x768"
        EndSubSection
        SubSection "Display"
                Depth     8
                Modes    "1024x768"
        EndSubSection
        SubSection "Display"
                Depth     16
                Modes    "1024x768"
        EndSubSection
EndSection

Section "DRI"
        Mode         0666
EndSection