Yeah my thoughts also, but in my whoo's search the forum for my Dell thread someone suggested this set up which worked. Either way the Dell requires the usb attachment for touch- I could just go the usb route minus the dp to hdmi(sorry forgot that part) but I get all kinds of blurry issues minus the DP.
Ah...ok...so you wanted to have touch on one of your external monitors. I am not sure I would want that on mine though. But it certainly sounds interesting.