Re: Quadro4 700XGL twinview problem - hardware issue?
The problem is your XF86Config file. First I'll tell a bit how the config file works and then I think you'll understand the problem.
The fundation of the config file is formed by the ServerLayout section. Unless others specified (custom option to startx for example) X uses the first ServerLayout it can find.
This section contains references to input (keyboard/mouse) and screen sections (and other stuff but that is less important). The most important of those sections is the Screen section which describes what Device (videocard), monitor, resolution and color depth to use.
As you copied nvidia's sample XF86Config it contains multiple ServerLayout sections. The first of them is called "AGP" and it describes a configuration with only one monitor. (cause of the problem you are seeing)
To fix the problem, keep only the needed ServerLayout section and also remove all unneeded screen sections so you get a simple XF86Config file.