From my reading it seams that the IC will eak out a few more ponies from your current turbo/intake/exhaust etc...but is simply not the bump in the pants that opening up your turbo outlet from a small hole to a high flow larger dimension DP.
Stock DP only lows the turbo to utilize a small part of its exit. Notice how much of the stock DP is blocked off. Only the pipe diameter itself is available to shove air through.
Aftermarket Divorced...now the turbo can get more air out faster which means we can get more air into the engine faster from the intake side....which means we can get more power. I course that's very basic conceptually, a little more complicated in reality.