Composite is not enabled. The following is the content of /etc/X11/xorg.conf, which fails. The changes to the original are framed by ###.
Section “ServerLayout”
Identifier “aticonfig Layout”
Screen 0 “aticonfig-Screen[0]-0” 0 0
Screen “amdcccle-Screen[6]-1” 1920 0
EndSection
Section “Module”
EndSection
Section “ServerFlags”
Option “Xinerama” “on”
EndSection
Section “Monitor”
Identifier “aticonfig-Monitor[0]-0”
Option “VendorName” “ATI Proprietary Driver”
Option “ModelName” “Generic Autodetecting Monitor”
Option “DPMS” “true”
EndSection
Section “Monitor”
Identifier “0-DFP3”
Option “VendorName” “ATI Proprietary Driver”
Option “ModelName” “Generic Autodetecting Monitor”
Option “DPMS” “true”
Option “PreferredMode” “1920x1080”
Option “TargetRefresh” “60”
Option “Position” “0 0”
Option “Rotate” “normal”
Option “Disable” “false”
SubSection "Extensions"
Option "Damage" "true"
Option "Composite" "true"
EndSubSection
EndSection
Section “Monitor”
Identifier “0-DFP4”
Option “VendorName” “ATI Proprietary Driver”
Option “ModelName” “Generic Autodetecting Monitor”
Option “DPMS” “true”
Option “PreferredMode” “1920x1080”
Option “TargetRefresh” “60”
Option “Position” “0 0”
Option “Rotate” “normal”
Option “Disable” “false”
SubSection "Extensions"
Option "Damage" "true"
Option "Composite" "true"
EndSubSection
EndSection
Section “Device”
Identifier “aticonfig-Device[0]-0”
Driver “fglrx”
Option “Monitor-DFP3” “0-DFP3”
BusID “PCI:6:0:0”
EndSection
Section “Device”
Identifier “amdcccle-Device[6]-1”
Driver “fglrx”
Option “Monitor-DFP4” “0-DFP4”
BusID “PCI:6:0:0”
Screen 1
EndSection
Section “Screen”
Identifier “aticonfig-Screen[0]-0”
Device “aticonfig-Device[0]-0”
DefaultDepth 24
SubSection “Display”
Viewport 0 0
Depth 24
EndSubSection
EndSection
Section “Screen”
Identifier “amdcccle-Screen[6]-1”
Device “amdcccle-Device[6]-1”
DefaultDepth 24
SubSection “Display”
Viewport 0 0
Depth 24
EndSubSection
EndSection