For the cost of the Denon mic. You would be better off buying a Radio Shack SPL meter.
However, obviously with the Denon mic - you will be able to do the auto-calibration.
But I will tell you now, that the Denon auto calibration is not the best in the business.
And that you would get better results with a manual calibration and a RS meter.
In very simple terms - A crossover is a filter (for audio).
Audio crossovers are a class of electronic filters designed specifically for use in audio applications, especially hi-fi. A commonly used dynamic loudspeaker driver is incapable of covering the entire audio spectrum all by itself. Thus, crossovers serve the purpose of splitting the audio signal into separate frequency bands which can be handled by individual loudspeaker drivers optimised for those bands. A combination of multiple drivers each catering to a different frequency band constitutes most hi-fi speaker systems.
To read more on crossovers in general terms and probably a little more than you want to know read here
http://en.wikipedia.org/wiki/Audio_crossover
