Displayport plus usb monitors

[genel]

My SCS computer has a displayport adapter with three displayport connectors. I have the main display and a projector using these ports. But in my ignorance of the features of displayport, when I added two more projectors I just bought a couple of usb to vga adapters.

Each of the displays worked fine individualy with SCS and I was a happy camper until last week when I tried to run all three projectors at once. Then SCS seemed hopelessly confused. No amount of futzing would get the projector on the DisplayPort to work at the same time as the USB projectors.

Different sequences of turning on projectors restarting SCS and/or playing with the video config would either have the image being sent to the DP projector lost in cyberspace, or appearing on one of the USB projectors.

So my first question is, is this even possible? That I run the USB projectors simultaeneously with the DP projector?

Or should I get a displayport hub and run the two new projectors off that?

[genel]

FWIW, I disconnected all the displays and started over, I reconnected all the displays, and relinked them to the primary display. Hard to tell what effect that has. Then in SCS I looked at the video setup and changed to the default video driver. Which had the effect of disabling the very useful 'preview' feature. But, amazingly, everything worked. I got through the rehearsal with the displays being misaligned but working.

I still don't "get" what I did to get it to work.