Multiple video cards

[Warren Block]

Test system:

FreeBSD 10-STABLE amd64 r269160
AMD A8-3850 APU (Radeon HD6550D)
Radeon X1650 PCIe card

Under IGX Configuration, the APU motherboard BIOS has a "Surround View" 
setting.  When enabled, the onboard HD6550 GPU remains enabled when an 
additional video card is connected.

With the HD6550 disabled, the X1650 works fine.  pciconf shows only one 
video device.

With the HD6550 enabled, both video devices show in pciconf, and X gives 
the "screens not found" error unless both are defined in xorg.conf.  X 
starts, but xrandr only shows the HD6550, and only the monitors attached 
to the motherboard video connectors work.  xrandr only shows that cards.

There may be more settings required in xorg.conf.  I think that Xinerama 
is obsolete, but don't know.

Based on some Linux stuff:
% xrandr --listproviders
RandR 1.4 not supported

Is there a right way to define multiple monitors on more than one card 
for the same virtual screen?