Since you already know about sisctrl, why aren't you using it for the task you want to accomplish? (Switching between output devices)
It is certainly beyond the scope of the debian config tools to provide a (at least somewhat sane) mechanism to add driver-specific options I would presume.
"vi /etc/X11/XF86Config-4" is the way to go here. Thomas -- Thomas Winischhofer Vienna/Austria thomas AT winischhofer DOT net *** http://www.winischhofer.net/ twini AT xfree86 DOT org