simple things first, are you pointing your miners at different cards? ie, when you run just polcbm it will tell you that you have to give it a device, usually 0 and 1. You then have to start each miner with a -d0 and a -d1 to use the second card. I like to open a separate terminal for each miner so I can watch them, and usually have 1 or 2 more open to watch temps, etc.
Also, if it's a dedicated miner (not a part time gamer) take out the xfire bridge, it doesn't help ( maybe even hinders.. ) mining.

edit:
now that I've thought about it and come back, I'm thinkin it is the xfire setup.. I'd start there by taking it out.