If a flat frequency curve is what one is after, then calibrating the system is important. Without specific sound generating equipment that we know is flat, it's not possible to calibrate the microphone.

WinSpeakerz by True Audio is a product that is fairly inexpensive, and will also provide the much needed design help when designing the speaker enclosure using the Theil/Small parameters.

The ECM8000 microphone from Behringer is an excellent microphone. It's inexpensive, and it's response curve is flat, +/- a few dB, until it actually gets to 20Khz, then there's a little 2.5dB bump.

I agree with the concept of adjusting a sound system for listening pleasure. I adjust my systems for a flat response, that way the music I'm listening to is the way the recording engineer intended it. I then use the tone controls on the head unit to tailor it to my own particular taste.

If the sound system is anything other than flat, it's harder to adjust the sound to my own taste, IMO.