ProTrader1,
I have no idea why your second monitor displays an image of lesser quality, unless your dual card sucks.
I have two computers, one with a dual-card Matrox G450, one with a dual-card ATI Radeon VE (both AGP). In both cases the secondary monitor is noticably softer than the primary monitor. I've tried switching the monitors around, and various permutations, always with the same results. All my monitors are Samsung 955DF and when they are the primary monitor the image quality, corner to corner, is superb.