Looks like the USB video card idea isn't a very dependable one. I had my displays go off while it redetected the DisplayLink adapters in the middle of stuff I was doing. Unacceptable for trading, in my opinion.
Also, with the usb display adapters it takes (I timed it) 4 minutes to finish booting, because it has to initialize each display adapter each time you boot. Initializing six displays from usb takes a while. Ok in a pinch maybe, but not ideal.
I got a firepro 2460 and it boots fast now, and works pretty much as I'd want it to. I'm getting a second one to power the rest of my displays, though it will be a few days before it gets here.
The 2260 adapters I got on ebay don't play nice with the 2460 by the looks, it wants both of them to run on the same driver, yet they use different drivers so pairing these didn't seem to work.
I'll see how it is with two 2460's, but I expect they will work nicely together.