My setup. Works like a charm with two Dell 22" LCD's.
(Edit - Note: this is running OpenBSD-CURRENT. There has been a lot of work going into radeon lately, so I'm not sure if 4.9 has everything you need for this to work).
Code:
$ dmesg | grep ATI
vga1 at pci1 dev 0 function 0 "ATI Radeon HD 3450" rev 0x00
Code:
Section "Device"
Identifier "Card0"
Driver "radeonhd"
BusID "PCI:1:0:0"
Option "LVDSProbePLL" "true"
Option "monitor-DVI-0" "Monitor0"
Option "monitor-DVI-1" "Monitor1"
Option "Int10" "true"
EndSection
Section "Screen"
Identifier "Screen0"
Device "Card0"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1680x1050"
Virtual 3840 3840
EndSubSection
EndSection
Code:
$ cat .xinitrc
xrandr --output DVI-I_1/digital --right-of DVI-I_2/digital