deloptes composed on 2015-12-24 01:11 (UTC+0100):
...you can start with Xorg setup
Xorg --help
... -configure probe for devices and write an xorg.conf
...
then run
Xorg -configure
OP is running Wheezy. Wheezy is like most distros of the Xorg automagic years. Its 'Xorg -configure' generates an xorg.conf loaded with litter unrelated to solving multihead trouble or any other kind of video trouble, and virtually nothing useful in actually generating a usable multihead config.[1] It's a skeleton that needs to be heavily stripped, and then extensivly built upon. A completely generic skeleton or template provides a better starting point for self-construction of a working multihead configuration.[2]
[1] http://fm.no-ip.com/Tmp/Linux/Xorg/xorg.conf.wheezynew-fromXorg-configure [2] e.g. http://fm.no-ip.com/Share/Linux/xorg.conf-intel-vga1600x1200under-digi1600x1...