With differential inputs the two inputs are SUBTRACTED (the word "differential" is from the root "difference"), NOT summed.
When the plus input is 2.048 volts HIGHER than the minus input, that's +2.048. When the plus input is 2.048 volts LOWER than the minus input, that's -2.048. So, you could have the plus input at 3.048, and the minus input at 1.0, or reversed, and you'd get the +/- input range without exceeding either supply rail. Your COMMON MODE voltage (look it up) is usually set midway between the supplies, so that for, say, a 5V VCC your differential range could be +/- 2.5V