O Xubuntu não reconhece a segunda placa gráfica ATI idêntica

Question

Eu tenho 2 placas gráficas ATI e 4 LCDs Samsung idênticos (2xDVI em cada cartão, sem fogo cruzado embora a ponte esteja conectada), e espero configurá-los da seguinte maneira.

Atualmente, o LCD 1 e 2 funcionam, no entanto, 3 e 4 não são reconhecidos. Eu dual boot Windows 7 e todos os 4 LCDs funcionam bem neste arranjo, então eu acho que as regras de qualquer configuração incorreta BIOS fora. Não tenho certeza se os drivers fglrx estão se registrando para o segundo cartão.

$ fglrxinfo
display: :0.0  screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: AMD Radeon HD 6800 Series
OpenGL version string: 4.2.11903 Compatibility Profile Context

$ lspci | grep VGA
01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Barts XT [Radeon HD 6800 Series]
02:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Barts XT [Radeon HD 6800 Series]

$ grep 'Output.*connected' /var/log/Xorg.0.log
[     5.160] (II) RADEON(0): Output DisplayPort-0 disconnected
[     5.160] (II) RADEON(0): Output HDMI-0 disconnected
[     5.160] (II) RADEON(0): Output DVI-0 connected
[     5.160] (II) RADEON(0): Output DVI-1 connected


$ cat /etc/X11/xorg.conf
# --------------------------------
# CARD1 --------------------------
# --------------------------------

# DEVICES -----------------------
Section "Device"
    Identifier  "Card1"
    Driver      "fglrx"
    Option      "Monitor-DFP6" "Left"
    Option      "Monitor-DFP7" "Center"
    BusID       "PCI:1:0:0"
EndSection

# MONITORS -----------------------
Section "Monitor"
    Identifier   "Left"
    Option      "VendorName" "Samsung"
    Option      "ModelName" "BX2450"
    Option      "DPMS" "true"
    Option      "PreferredMode" "1920x1080"
    Option      "TargetRefresh" "60"
    #Option     "Position" "0 0"
    Option      "Rotate" "normal"
    Option      "Disable" "false"
EndSection

Section "Monitor"
    Identifier   "Center"
    Option      "VendorName" "Samsung"
    Option      "ModelName" "BX2450"
    Option      "DPMS" "true"
    Option      "PreferredMode" "1920x1080"
    Option      "TargetRefresh" "60"
    #Option     "Position" "1920 0"
    Option      "Rotate" "normal"
    Option      "Disable" "false"
EndSection

# SCREENS -----------------------
Section "Screen"
    Identifier "ScreenLeft"
    Device     "Card1"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Virtual   1920 1080
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "ScreenCenter"
    Device     "Card1"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Virtual   1920 1080
        Depth     24
    EndSubSection
EndSection

# --------------------------------
# CARD2 --------------------------
# --------------------------------

# DEVICES -----------------------
Section "Device"
    Identifier  "Card2"
    Driver      "fglrx"
    Option      "Monitor-DFP6" "Right"
    Option      "Monitor-DFP7" "Top"
    BusID       "PCI:2:0:0"
EndSection

# MONITORS -----------------------
Section "Monitor"
    Identifier   "Right"
    Option      "VendorName" "Samsung"
    Option      "ModelName" "BX2450"
    Option      "DPMS" "true"
    Option      "PreferredMode" "1920x1080"
    Option      "TargetRefresh" "60"
    #Option     "Position" "3840 0"
    Option      "Rotate" "normal"
    Option      "Disable" "false"
EndSection

Section "Monitor"
    Identifier   "Top"
    Option      "VendorName" "Samsung"
    Option      "ModelName" "BX2450"
    Option      "DPMS" "true"
    Option      "PreferredMode" "1920x1080"
    Option      "TargetRefresh" "60"
    #Option     "Position" "1920 1080"
    Option      "Rotate" "normal"
    Option      "Disable" "false"
EndSection

# SCREENS -----------------------
Section "Screen"
    Identifier "ScreenRight"
    Device     "Card2"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Virtual   1920 1080
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "ScreenTop"
    Device     "Card2"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Virtual   1920 1080
        Depth     24
    EndSubSection
EndSection

# --------------------------------
# SERVER -------------------------
# --------------------------------
Section "ServerLayout"
    Identifier     "myLayout"
    Screen      "ScreenLeft" 0 0
    Screen      "ScreenCenter" 1920 0
    Screen      "ScreenRight" 3840 0
    Screen      "ScreenTop" 1920 1080
EndSection

Section "ServerFlags"
    #Option     "Xinerama" "on"
EndSection