Let's see the loopback graph.'ripples' on the loop-back measurement from my audigy 2 zs
Not at all. This interface is the same as all line level interfaces, it's a high impedance connection, where the output impedance of the source is usually in the order of 50 ohms to 150 ohms and the input impedance of the load is in the order of 10Kohms to 50Kohms.since the microphone (preamp) to sound card will have a different impedance setup than the sound card loop-back setup, will that not affect the determined frequency response?
This is known as a voltage bridge connection where the preamp is acting as a voltage source and almost no current is drawn. Large variations in impedance have no appreciable effect on the response.