Well, after a few days more of putzing, I finally got things set up correctly. I keep forgetting to leave my workstation on during the day so I can download the config for XF86Conf and show it on this post, so the written details will have to wait. Suffice it to say, however, that syntax and the whole -scanpci switch were my main issues. Firstly, running
XFree86 -scanpci
never did work. I already knew that the Matrox G450 AGP card was sitting at PCI:1:0:0, but what I didn't realize is that each head is not shown with a different PCI definition. In fact, the more I think about it, the more that makes sense - how would the system see a single card represented by two bus connections? Anyway, the BusID part of XF86Config remains
BusID PCI:1:0:0
and the rest is defined by a Screen X deffinition.
Secondly, if you do not pay attention to your syntax, your life will be a living hell. What makes problems worse is that there are 14 ways to skin a cat... and usually you cannot mix and match.
I will post the config file as soon as possible. Email me with any questions or make comments below!